[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"playground-css-nesting-sass-replaced":3,"verticals":17},{"slug":4,"title":5,"summary":6,"html":7,"css":8,"js":9,"config":10,"doc":13},"css-nesting-sass-replaced","Native CSS nesting — interactive playground",null,"\u003Cdiv class=\"pg\">\n    \u003Ch1 class=\"pg-title\">🧩 Native CSS nesting — write nested, watch it flatten\u003C\u002Fh1>\n    \u003Cp class=\"pg-sub\">\n      Edit the nested CSS on the left. Watch \u003Ccode>&\u003C\u002Fcode> expand differently depending on\n      what follows it — live, in both the flattened CSS and a genuinely rendered card.\n    \u003C\u002Fp>\n\n    \u003Cdiv class=\"banner\" id=\"supportBanner\">\u003C\u002Fdiv>\n\n    \u003Cdiv class=\"layout\">\n      \u003Cdiv class=\"panel\">\n        \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">1\u003C\u002Fspan> Nested CSS — edit me\u003C\u002Fdiv>\n        \u003Clabel class=\"ctl-label\" for=\"src\" style=\"display:block; margin-bottom:6px;\">Source\u003C\u002Flabel>\n        \u003Ctextarea id=\"src\" spellcheck=\"false\" autocapitalize=\"off\" autocorrect=\"off\" rows=\"14\" aria-describedby=\"srcHint\">\u003C\u002Ftextarea>\n        \u003Cdiv class=\"presets\" style=\"margin-top:12px\">\n          \u003Cbutton class=\"btn sm\" type=\"button\" data-preset=\"card\">Card (default)\u003C\u002Fbutton>\n          \u003Cbutton class=\"btn sm\" type=\"button\" data-preset=\"mistake\">The &__child mistake\u003C\u002Fbutton>\n        \u003C\u002Fdiv>\n        \u003Cdiv class=\"btn-row\" style=\"margin-top:10px\">\n          \u003Cbutton class=\"btn ghost sm\" type=\"button\" id=\"reset\">Reset\u003C\u002Fbutton>\n        \u003C\u002Fdiv>\n        \u003Cp class=\"hint\" id=\"srcHint\">Type here. Every keystroke re-flattens the CSS below and re-renders the card at the bottom — nothing is precomputed.\u003C\u002Fp>\n      \u003C\u002Fdiv>\n\n      \u003Cdiv class=\"col\">\n        \u003Cdiv class=\"panel\">\n          \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">2\u003C\u002Fspan> What each form expands to\u003C\u002Fdiv>\n          \u003Cdiv class=\"seg\" id=\"kindSeg\" role=\"group\" aria-label=\"Highlight a nesting form\">\n            \u003Cbutton type=\"button\" data-kind=\"all\" aria-pressed=\"true\">All\u003C\u002Fbutton>\n            \u003Cbutton type=\"button\" data-kind=\"modifier\" aria-pressed=\"false\">&\u003C\u002Fbutton>\n            \u003Cbutton type=\"button\" data-kind=\"explicit-descendant\" aria-pressed=\"false\">& .child\u003C\u002Fbutton>\n            \u003Cbutton type=\"button\" data-kind=\"implicit-descendant\" aria-pressed=\"false\">.child\u003C\u002Fbutton>\n            \u003Cbutton type=\"button\" data-kind=\"pseudo\" aria-pressed=\"false\">&:hover\u003C\u002Fbutton>\n          \u003C\u002Fdiv>\n          \u003Cp class=\"hint\" id=\"kindCaption\">Pick a form above to see exactly what it compiles to, highlighted on the right.\u003C\u002Fp>\n        \u003C\u002Fdiv>\n\n        \u003Cdiv class=\"panel\">\n          \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">3\u003C\u002Fspan> Compiled \u002F flattened CSS\u003C\u002Fdiv>\n          \u003Cdiv class=\"code\" id=\"compiled\" aria-live=\"polite\">\u003C\u002Fdiv>\n          \u003Cp class=\"hint\">This is a plain-text illustration of what the browser resolves internally — it is not what runs the preview below.\u003C\u002Fp>\n        \u003C\u002Fdiv>\n\n        \u003Cdiv class=\"panel\">\n          \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">4\u003C\u002Fspan> Live preview — real browser nesting, not a simulation\u003C\u002Fdiv>\n          \u003Cdiv class=\"row between\" style=\"margin-bottom:10px; gap:10px;\">\n            \u003Cdiv class=\"seg\" id=\"viewportSeg\" role=\"group\" aria-label=\"Preview viewport width\">\n              \u003Cbutton type=\"button\" data-vp=\"wide\" aria-pressed=\"true\">Wide (≥480px)\u003C\u002Fbutton>\n              \u003Cbutton type=\"button\" data-vp=\"narrow\" aria-pressed=\"false\">Narrow (<480px)\u003C\u002Fbutton>\n            \u003C\u002Fdiv>\n            \u003Clabel class=\"toggle\">\n              \u003Cinput type=\"checkbox\" id=\"featuredToggle\" \u002F>\u003Cspan class=\"switch\">\u003C\u002Fspan>\n              \u003Cspan>Featured (&.card--featured)\u003C\u002Fspan>\n            \u003C\u002Flabel>\n          \u003C\u002Fdiv>\n          \u003Cdiv class=\"stage-wrap\" id=\"stageWrap\">\n            \u003Ciframe id=\"stageFrame\" title=\"Live rendered card, styled by your nested CSS\" scrolling=\"no\">\u003C\u002Fiframe>\n          \u003C\u002Fdiv>\n          \u003Cdiv class=\"status\" id=\"parseStatus\" style=\"margin-top:12px\">\n            \u003Cspan class=\"dot good\" id=\"parseDot\">\u003C\u002Fspan>\u003Cspan id=\"parseText\">Parsed OK — updated live.\u003C\u002Fspan>\n          \u003C\u002Fdiv>\n          \u003Cp class=\"hint\">The card above renders inside a real sandboxed page using your exact nested CSS — the browser is doing the parsing, nothing here is faked. Toggle the viewport width to trigger the nested \u003Ccode>@media\u003C\u002Fcode> query.\u003C\u002Fp>\n        \u003C\u002Fdiv>\n      \u003C\u002Fdiv>\n    \u003C\u002Fdiv>\n  \u003C\u002Fdiv>\n\n\u003Cscript>\n  \"use strict\";\n  const $ = (id) => document.getElementById(id);\n\n  const srcEl = $(\"src\");\n  const compiledEl = $(\"compiled\");\n  const frame = $(\"stageFrame\");\n  const stageWrap = $(\"stageWrap\");\n  const kindSeg = $(\"kindSeg\");\n  const kindCaption = $(\"kindCaption\");\n  const viewportSeg = $(\"viewportSeg\");\n  const featuredToggle = $(\"featuredToggle\");\n  const parseDot = $(\"parseDot\");\n  const parseText = $(\"parseText\");\n  const supportBanner = $(\"supportBanner\");\n\n  let currentKind = \"all\";\n  let debounceTimer = null;\n\n  const DEFAULT_CSS =\n`.card {\n  padding: 1.5rem;\n  border-radius: 10px;\n  background: var(--surface);\n\n  &:hover {\n    background: var(--surface-hover);\n  }\n\n  & .card__title {\n    font-weight: 700;\n  }\n\n  .card__meta {\n    color: var(--muted);\n  }\n\n  &.card--featured {\n    border: 2px solid var(--accent);\n  }\n\n  @media (min-width: 480px) {\n    padding: 2rem;\n  }\n}`;\n\n  const MISTAKE_CSS =\n`.card {\n  padding: 1.5rem;\n  background: var(--surface);\n\n  &__title {\n    font-weight: 700;\n    color: var(--accent);\n  }\n}`;\n\n  const CAPTIONS = {\n    all: \"Pick a form above to see exactly what it compiles to, highlighted on the right.\",\n    modifier: \"& fused directly to a class, ID, or pseudo — nothing in between — stays on the SAME element. &.card--featured → .card.card--featured: one element, two classes, no space.\",\n    \"explicit-descendant\": \"& followed by a space, then a selector, is an explicit descendant combinator. & .card__title → .card .card__title — matches that class anywhere inside .card.\",\n    \"implicit-descendant\": \"Leave & off entirely and nesting still assumes a descendant. .card__meta → .card .card__meta — exactly the same result as writing & .card__meta.\",\n    pseudo: \"& glued straight to a pseudo-class fuses onto the same element too, just like Sass. &:hover → .card:hover.\",\n  };\n\n  const FRAME_HTML =\n`\u003C!doctype html>\u003Chtml>\u003Chead>\u003Cmeta charset=\"utf-8\">\n\n\u003C\u002Fhead>\n\u003Cbody>\n  \u003Cdiv class=\"card\">\n    \u003Cp class=\"card__title\">Card title\u003C\u002Fp>\n    \u003Cp class=\"card__meta\">Edit the CSS on the left — this card is real, sandboxed HTML.\u003C\u002Fp>\n  \u003C\u002Fdiv>","\u002F*\n * Shared playground design system — daily-post\n * ============================================\n * Link it from any post's playground\u002Findex.html (no per-post boilerplate):\n *\n *   \u003Clink rel=\"stylesheet\" href=\"..\u002F..\u002F..\u002Fplayground\u002Fassets\u002Fbase.css\" \u002F>\n *\n * The relative path resolves the same locally (posts\u002F\u003Cbase>\u002Fplayground\u002F) and on\n * the deployed host (public\u002Fposts\u002F\u003Cbase>\u002Fplayground\u002F), because build-site.js\n * mirrors this file to public\u002Fplayground\u002Fassets\u002Fbase.css. For a CodeSandbox\n * --embed, playground.js inlines this file so the single-file sandbox still styles.\n *\n * Then write ONLY the demo-specific CSS in your inline \u003Cstyle>. Everything below\n * — tokens, layout, panels, buttons, toggles, sliders, code blocks, status\u002Flog,\n * banners, presets — comes for free and looks consistent across every post.\n *\n * Theme-aware: dark by default, light via prefers-color-scheme AND a\n * [data-theme] override on \u003Chtml> (so a toggle can force either). Accessible:\n * real focus rings, adequate contrast, reduced-motion honored.\n *\u002F\n\n\u002F* ---------- design tokens ---------- *\u002F\n:root {\n  --bg: #0d1117;\n  --bg-grid: #ffffff0a;\n  --panel: #161b22;\n  --panel-2: #0b0e14;\n  --card: #0b0e14;\n  --ink: #e8ebf2;\n  --muted: #9aa4b2;\n  --faint: #6b7688;\n  --line: #232a35;\n  --line-soft: #ffffff12;\n  --accent: #7c9cff;\n  --accent-ink: #0b0e14;\n  --good: #3fb950;\n  --warn: #f0883e;\n  --bad: #f85149;\n  --info: #58a6ff;\n  --radius: 14px;\n  --radius-sm: 9px;\n  --shadow: 0 8px 30px #0006;\n  --shadow-sm: 0 4px 14px #0005;\n  --mono: ui-monospace, SFMono-Regular, \"SF Mono\", Menlo, Consolas, \"Liberation Mono\", monospace;\n  --sans: ui-sans-serif, system-ui, -apple-system, \"Segoe UI\", Roboto, \"Helvetica Neue\", sans-serif;\n  color-scheme: dark;\n}\n\n\u002F* Light theme — system preference, overridable by [data-theme] on \u003Chtml>. *\u002F\n@media (prefers-color-scheme: light) {\n  :root:not([data-theme=\"dark\"]) {\n    --bg: #f4f6fb;\n    --bg-grid: #00000008;\n    --panel: #ffffff;\n    --panel-2: #f0f3f9;\n    --card: #f7f9fc;\n    --ink: #131722;\n    --muted: #5b6472;\n    --faint: #8a93a3;\n    --line: #e2e7f0;\n    --line-soft: #00000010;\n    --accent: #2f6df0;\n    --accent-ink: #ffffff;\n    --good: #1a7f37;\n    --warn: #bc4c00;\n    --bad: #cf222e;\n    --info: #0969da;\n    --shadow: 0 8px 30px #0000001f;\n    --shadow-sm: 0 4px 14px #00000014;\n    color-scheme: light;\n  }\n}\n:root[data-theme=\"light\"] {\n  --bg: #f4f6fb;\n  --bg-grid: #00000008;\n  --panel: #ffffff;\n  --panel-2: #f0f3f9;\n  --card: #f7f9fc;\n  --ink: #131722;\n  --muted: #5b6472;\n  --faint: #8a93a3;\n  --line: #e2e7f0;\n  --line-soft: #00000010;\n  --accent: #2f6df0;\n  --accent-ink: #ffffff;\n  --good: #1a7f37;\n  --warn: #bc4c00;\n  --bad: #cf222e;\n  --info: #0969da;\n  --shadow: 0 8px 30px #0000001f;\n  --shadow-sm: 0 4px 14px #00000014;\n  color-scheme: light;\n}\n\n\u002F* ---------- reset & base ---------- *\u002F\n*, *::before, *::after { box-sizing: border-box; }\n\nbody {\n  margin: 0;\n  min-height: 100vh;\n  font-family: var(--sans);\n  color: var(--ink);\n  background:\n    radial-gradient(circle at 1px 1px, var(--bg-grid) 1px, transparent 0) 0 0 \u002F 24px 24px,\n    var(--bg);\n  display: flex;\n  justify-content: center;\n  align-items: flex-start;\n  padding: clamp(14px, 3vw, 26px);\n  line-height: 1.55;\n  -webkit-font-smoothing: antialiased;\n  text-rendering: optimizeLegibility;\n}\n\n\u002F* The single content column. *\u002F\n.pg {\n  width: 100%;\n  max-width: 860px;\n}\n\n\u002F* ---------- header ---------- *\u002F\n.pg-title {\n  font-size: clamp(1.15rem, 1rem + 1vw, 1.4rem);\n  font-weight: 800;\n  letter-spacing: -0.02em;\n  margin: 0 0 4px;\n  display: flex;\n  align-items: center;\n  gap: 9px;\n}\n.pg-sub {\n  color: var(--muted);\n  font-size: 0.92rem;\n  line-height: 1.5;\n  margin: 0 0 16px;\n  max-width: 66ch;\n}\n.pg-sub strong, .pg-sub b { color: var(--ink); font-weight: 700; }\n.pg-sub code { font-family: var(--mono); background: var(--line-soft); color: var(--accent);\n  padding: 1px 6px; border-radius: 6px; font-size: 0.85em; }\n\n\u002F* ---------- panels ---------- *\u002F\n.panel {\n  background: var(--panel);\n  border: 1px solid var(--line);\n  border-radius: var(--radius);\n  padding: 16px 18px;\n  margin-bottom: 14px;\n  box-shadow: var(--shadow-sm);\n}\n.panel-label {\n  font-size: 0.7rem;\n  text-transform: uppercase;\n  letter-spacing: 0.08em;\n  color: var(--muted);\n  font-weight: 800;\n  margin: 0 0 13px;\n  display: flex;\n  align-items: center;\n  gap: 8px;\n}\n.panel-label .n {\n  display: inline-grid; place-items: center;\n  width: 18px; height: 18px; border-radius: 50%;\n  background: var(--accent); color: var(--accent-ink);\n  font-size: 0.66rem; font-weight: 800;\n}\n\n\u002F* ---------- layout helpers ---------- *\u002F\n.row { display: flex; flex-wrap: wrap; gap: 12px; align-items: center; }\n.row.between { justify-content: space-between; }\n.col { display: flex; flex-direction: column; gap: 10px; }\n.grow { flex: 1 1 0; min-width: 0; }\n.wrap-controls { display: flex; flex-wrap: wrap; gap: 16px 24px; align-items: flex-end; }\n.field { display: flex; flex-direction: column; gap: 7px; min-width: 0; }\n.field > .label, .ctl-label {\n  font-size: 0.7rem; text-transform: uppercase; letter-spacing: 0.04em;\n  color: var(--muted); font-weight: 800;\n}\n\n\u002F* ---------- buttons ---------- *\u002F\n.btn {\n  font: inherit; font-weight: 650; font-size: 0.88rem;\n  cursor: pointer; user-select: none;\n  border: 1px solid var(--line);\n  background: var(--card); color: var(--ink);\n  padding: 9px 15px; border-radius: var(--radius-sm);\n  display: inline-flex; align-items: center; gap: 8px;\n  transition: background .15s ease, border-color .15s ease, transform .05s ease, color .15s ease;\n}\n.btn:hover { background: var(--line-soft); border-color: var(--muted); }\n.btn:active { transform: translateY(1px); }\n.btn:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }\n.btn[disabled] { opacity: 0.45; cursor: not-allowed; }\n.btn.primary { background: var(--accent); border-color: var(--accent); color: var(--accent-ink); }\n.btn.primary:hover { filter: brightness(1.08); background: var(--accent); }\n.btn.good { background: var(--good); border-color: var(--good); color: #04140a; }\n.btn.bad  { background: var(--bad);  border-color: var(--bad);  color: #fff; }\n.btn.ghost { background: transparent; }\n.btn.sm { padding: 6px 11px; font-size: 0.82rem; }\n\n.btn-row { display: flex; flex-wrap: wrap; gap: 9px; }\n\n\u002F* Segmented control — a row of buttons where one is active (aria-pressed). *\u002F\n.seg { display: inline-flex; background: var(--card); border: 1px solid var(--line);\n  border-radius: var(--radius-sm); padding: 3px; gap: 3px; }\n.seg button {\n  font: inherit; font-weight: 650; font-size: 0.84rem; cursor: pointer;\n  border: none; background: transparent; color: var(--muted);\n  padding: 7px 13px; border-radius: 7px;\n  transition: background .15s ease, color .15s ease;\n}\n.seg button:hover { color: var(--ink); }\n.seg button[aria-pressed=\"true\"] { background: var(--accent); color: var(--accent-ink); }\n.seg button:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }\n\n\u002F* Preset chips — worked-example shortcuts. *\u002F\n.presets { display: flex; flex-wrap: wrap; gap: 8px; }\n.presets .btn { background: var(--panel-2); }\n\n\u002F* ---------- toggle switch ---------- *\u002F\n.toggle { display: inline-flex; align-items: center; gap: 10px; cursor: pointer;\n  font-size: 0.88rem; font-weight: 600; user-select: none; }\n.toggle input { position: absolute; opacity: 0; width: 0; height: 0; }\n.switch { position: relative; width: 44px; height: 25px; border-radius: 999px; flex: none;\n  background: var(--line); border: 1px solid var(--line); transition: background .18s ease; }\n.switch::after { content: \"\"; position: absolute; top: 2px; left: 2px; width: 19px; height: 19px;\n  border-radius: 50%; background: #cfd6e4; transition: transform .18s ease; box-shadow: 0 1px 3px #0006; }\n.toggle input:checked + .switch { background: var(--good); border-color: var(--good); }\n.toggle input:checked + .switch::after { transform: translateX(19px); background: #fff; }\n.toggle input:focus-visible + .switch { outline: 2px solid var(--accent); outline-offset: 2px; }\n\n\u002F* ---------- range slider ---------- *\u002F\ninput[type=\"range\"] {\n  -webkit-appearance: none; appearance: none; width: 100%; height: 6px;\n  background: var(--line); border-radius: 999px; outline: none; cursor: pointer; margin: 8px 0;\n}\ninput[type=\"range\"]::-webkit-slider-thumb {\n  -webkit-appearance: none; appearance: none; width: 19px; height: 19px; border-radius: 50%;\n  background: var(--accent); border: 2px solid var(--panel); box-shadow: var(--shadow-sm); cursor: pointer;\n}\ninput[type=\"range\"]::-moz-range-thumb {\n  width: 19px; height: 19px; border-radius: 50%; background: var(--accent);\n  border: 2px solid var(--panel); box-shadow: var(--shadow-sm); cursor: pointer;\n}\ninput[type=\"range\"]:focus-visible { outline: 2px solid var(--accent); outline-offset: 3px; }\n\n\u002F* ---------- text inputs \u002F selects ---------- *\u002F\ninput[type=\"text\"], input[type=\"number\"], input[type=\"search\"], select, textarea {\n  font: inherit; color: var(--ink); background: var(--card);\n  border: 1px solid var(--line); border-radius: var(--radius-sm); padding: 8px 11px; width: 100%;\n}\ntextarea { font-family: var(--mono); font-size: 0.85rem; line-height: 1.6; resize: vertical; }\ninput:focus-visible, select:focus-visible, textarea:focus-visible {\n  outline: 2px solid var(--accent); outline-offset: 1px; border-color: var(--accent);\n}\n\n\u002F* ---------- status \u002F output \u002F log ---------- *\u002F\n.status {\n  display: flex; align-items: center; gap: 9px; flex-wrap: wrap;\n  font-size: 0.9rem; font-weight: 600;\n  padding: 11px 14px; border-radius: var(--radius-sm);\n  background: var(--panel-2); border: 1px solid var(--line); color: var(--ink);\n}\n.status.good { border-color: color-mix(in srgb, var(--good) 55%, var(--line)); }\n.status.warn { border-color: color-mix(in srgb, var(--warn) 55%, var(--line)); }\n.status.bad  { border-color: color-mix(in srgb, var(--bad) 55%, var(--line)); }\n.dot { width: 9px; height: 9px; border-radius: 50%; background: var(--muted); flex: none; }\n.dot.good { background: var(--good); } .dot.warn { background: var(--warn); }\n.dot.bad { background: var(--bad); } .dot.info { background: var(--info); }\n\n.output { background: var(--panel-2); border: 1px solid var(--line); border-radius: var(--radius-sm);\n  padding: 13px 15px; }\n.log { font-family: var(--mono); font-size: 0.8rem; line-height: 1.7; background: var(--card);\n  border: 1px solid var(--line); border-radius: var(--radius-sm); padding: 11px 14px;\n  max-height: 220px; overflow-y: auto; white-space: pre-wrap; }\n\n\u002F* ---------- code block + syntax tokens ---------- *\u002F\n.code {\n  font-family: var(--mono); font-size: 0.82rem; line-height: 1.7;\n  background: var(--panel-2); border: 1px solid var(--line); border-radius: var(--radius-sm);\n  padding: 13px 15px; overflow-x: auto; white-space: pre; tab-size: 2;\n}\n.code .tok-sel  { color: var(--accent); }\n.code .tok-prop { color: #86e29b; }\n.code .tok-kw   { color: #ff9bcb; }\n.code .tok-str  { color: #f0c674; }\n.code .tok-num  { color: #f0883e; }\n.code .tok-cmt  { color: var(--faint); font-style: italic; }\n.code .hl { background: color-mix(in srgb, var(--good) 22%, transparent); border-radius: 4px; padding: 0 3px; }\n\n\u002F* ---------- hint \u002F caption ---------- *\u002F\n.hint { font-size: 0.83rem; color: var(--muted); line-height: 1.55; margin: 10px 0 0; }\n.hint code { font-family: var(--mono); color: var(--ink); background: var(--line-soft);\n  padding: 1px 5px; border-radius: 5px; font-size: 0.86em; }\n.hint strong { color: var(--ink); }\n\n\u002F* ---------- banner (feature-support \u002F notices) ---------- *\u002F\n.banner {\n  display: none; margin-bottom: 14px; padding: 11px 14px; border-radius: 11px;\n  font-size: 0.85rem; line-height: 1.5;\n  color: var(--ink); background: color-mix(in srgb, var(--warn) 12%, var(--panel));\n  border: 1px solid color-mix(in srgb, var(--warn) 45%, var(--line));\n}\n.banner.show { display: block; }\n.banner.info { background: color-mix(in srgb, var(--info) 12%, var(--panel));\n  border-color: color-mix(in srgb, var(--info) 45%, var(--line)); }\n.banner code { font-family: var(--mono); background: var(--line-soft); padding: 1px 5px; border-radius: 5px; }\n\n\u002F* ---------- misc atoms ---------- *\u002F\n.pill { display: inline-flex; align-items: center; gap: 6px; font-size: 0.75rem; font-weight: 700;\n  padding: 3px 9px; border-radius: 999px; background: var(--line-soft); color: var(--muted); }\n.pill.good { color: var(--good); background: color-mix(in srgb, var(--good) 16%, transparent); }\n.pill.bad  { color: var(--bad);  background: color-mix(in srgb, var(--bad) 16%, transparent); }\n.mono { font-family: var(--mono); }\n.muted { color: var(--muted); }\n.big-num { font-family: var(--mono); font-size: 1.6rem; font-weight: 800; letter-spacing: -0.02em; }\n\n\u002F* Optional theme toggle button (top-right). Wire it in JS if you want it. *\u002F\n.theme-btn { position: fixed; top: 12px; right: 12px; z-index: 20; }\n\n\u002F* ---------- responsive ---------- *\u002F\n@media (max-width: 560px) {\n  .panel { padding: 14px; }\n  .wrap-controls { gap: 14px; }\n  .btn { padding: 9px 13px; }\n}\n\n\u002F* ---------- reduced motion ---------- *\u002F\n@media (prefers-reduced-motion: reduce) {\n  *, *::before, *::after { transition-duration: 0.01ms !important; animation-duration: 0.01ms !important; }\n}\n\n\n\u002F* Demo-specific CSS ONLY. base.css already provides tokens, layout, panels,\n     buttons, toggles, sliders, code blocks, status\u002Flog, banners, presets. *\u002F\n\n  .layout { display: grid; grid-template-columns: 1fr; gap: 14px; }\n  @media (min-width: 780px) {\n    .layout { grid-template-columns: minmax(280px, 400px) 1fr; align-items: start; }\n  }\n\n  #src {\n    min-height: 230px;\n    font-size: 0.82rem;\n  }\n\n  \u002F* Compiled\u002Fflattened CSS readout — one .crule per resolved rule. *\u002F\n  #compiled { display: flex; flex-direction: column; gap: 0; }\n  .crule {\n    padding: 4px 6px;\n    margin: 0 0 4px;\n    border-radius: 6px;\n    transition: background .15s ease, opacity .15s ease;\n  }\n  .crule.hl { background: color-mix(in srgb, var(--good) 20%, transparent); }\n  .crule.dim { opacity: 0.32; }\n  .crule.invalid { color: var(--bad); }\n\n  \u002F* Live preview stage — a real sandboxed document, fixed widths so the\n     Wide\u002FNarrow toggle reliably straddles the nested @media breakpoint\n     regardless of the surrounding page size. *\u002F\n  .stage-wrap {\n    border: 1px dashed var(--line);\n    border-radius: var(--radius-sm);\n    background: var(--panel-2);\n    padding: 10px;\n    max-width: 560px;\n    margin: 0 auto;\n    transition: max-width .2s ease;\n  }\n  .stage-wrap.narrow { max-width: 300px; }\n  #stageFrame { width: 100%; height: 210px; border: 0; display: block; }\n\n:root { --surface:#161b22; --surface-hover:#1c2330; --accent:#7c9cff; --muted:#9aa4b2; --ink:#e8ebf2; }\n  * { box-sizing: border-box; }\n  html, body { margin:0; height:100%; }\n  body {\n    display:flex; align-items:center; justify-content:center;\n    min-height:100%; padding:18px; box-sizing:border-box;\n    font-family: ui-sans-serif, system-ui, -apple-system, \"Segoe UI\", Roboto, sans-serif;\n    color: var(--ink); background: transparent;\n  }\n  .card__title { font-size: 1.05rem; margin: 0 0 6px; }\n  .card__meta { font-size: 0.85rem; margin: 0; }","\"use strict\";\n  const $ = (id) => document.getElementById(id);\n\n  const srcEl = $(\"src\");\n  const compiledEl = $(\"compiled\");\n  const frame = $(\"stageFrame\");\n  const stageWrap = $(\"stageWrap\");\n  const kindSeg = $(\"kindSeg\");\n  const kindCaption = $(\"kindCaption\");\n  const viewportSeg = $(\"viewportSeg\");\n  const featuredToggle = $(\"featuredToggle\");\n  const parseDot = $(\"parseDot\");\n  const parseText = $(\"parseText\");\n  const supportBanner = $(\"supportBanner\");\n\n  let currentKind = \"all\";\n  let debounceTimer = null;\n\n  const DEFAULT_CSS =\n`.card {\n  padding: 1.5rem;\n  border-radius: 10px;\n  background: var(--surface);\n\n  &:hover {\n    background: var(--surface-hover);\n  }\n\n  & .card__title {\n    font-weight: 700;\n  }\n\n  .card__meta {\n    color: var(--muted);\n  }\n\n  &.card--featured {\n    border: 2px solid var(--accent);\n  }\n\n  @media (min-width: 480px) {\n    padding: 2rem;\n  }\n}`;\n\n  const MISTAKE_CSS =\n`.card {\n  padding: 1.5rem;\n  background: var(--surface);\n\n  &__title {\n    font-weight: 700;\n    color: var(--accent);\n  }\n}`;\n\n  const CAPTIONS = {\n    all: \"Pick a form above to see exactly what it compiles to, highlighted on the right.\",\n    modifier: \"& fused directly to a class, ID, or pseudo — nothing in between — stays on the SAME element. &.card--featured → .card.card--featured: one element, two classes, no space.\",\n    \"explicit-descendant\": \"& followed by a space, then a selector, is an explicit descendant combinator. & .card__title → .card .card__title — matches that class anywhere inside .card.\",\n    \"implicit-descendant\": \"Leave & off entirely and nesting still assumes a descendant. .card__meta → .card .card__meta — exactly the same result as writing & .card__meta.\",\n    pseudo: \"& glued straight to a pseudo-class fuses onto the same element too, just like Sass. &:hover → .card:hover.\",\n  };\n\n  const FRAME_HTML =\n`\u003C!doctype html>\u003Chtml>\u003Chead>\u003Cmeta charset=\"utf-8\">\u003Cstyle>\n  :root { --surface:#161b22; --surface-hover:#1c2330; --accent:#7c9cff; --muted:#9aa4b2; --ink:#e8ebf2; }\n  * { box-sizing: border-box; }\n  html, body { margin:0; height:100%; }\n  body {\n    display:flex; align-items:center; justify-content:center;\n    min-height:100%; padding:18px; box-sizing:border-box;\n    font-family: ui-sans-serif, system-ui, -apple-system, \"Segoe UI\", Roboto, sans-serif;\n    color: var(--ink); background: transparent;\n  }\n  .card__title { font-size: 1.05rem; margin: 0 0 6px; }\n  .card__meta { font-size: 0.85rem; margin: 0; }\n\u003C\u002Fstyle>\n\u003Cstyle id=\"dynamic\">\u003C\u002Fstyle>\n\u003C\u002Fhead>\n\u003Cbody>\n  \u003Cdiv class=\"card\">\n    \u003Cp class=\"card__title\">Card title\u003C\u002Fp>\n    \u003Cp class=\"card__meta\">Edit the CSS on the left — this card is real, sandboxed HTML.\u003C\u002Fp>\n  \u003C\u002Fdiv>\n\u003C\u002Fbody>\u003C\u002Fhtml>`;\n\n  \u002F\u002F ---------- tiny nested-CSS parser (subset: rules, decls, one level of @media) ----------\n  function stripComments(css) {\n    return css.replace(\u002F\\\u002F\\*[\\s\\S]*?\\*\\\u002F\u002Fg, (m) => m.replace(\u002F[^\\n]\u002Fg, \" \"));\n  }\n\n  function parseCSS(css) {\n    let i = 0;\n    const n = css.length;\n    function skipWs() { while (i \u003C n && \u002F\\s\u002F.test(css[i])) i++; }\n\n    function parseBlock(endChar) {\n      const nodes = [];\n      while (true) {\n        skipWs();\n        if (i >= n) break;\n        if (endChar && css[i] === endChar) { i++; break; }\n\n        if (css[i] === \"@\") {\n          const start = i;\n          let j = i;\n          while (j \u003C n && css[j] !== \"{\" && css[j] !== \";\") j++;\n          if (j >= n) { i = j; break; }\n          const header = css.slice(start, j).trim();\n          if (css[j] === \";\") { i = j + 1; continue; }\n          i = j + 1;\n          const body = parseBlock(\"}\");\n          nodes.push({ type: \"atrule\", header, body });\n          continue;\n        }\n\n        const start = i;\n        let j = i;\n        let depth = 0;\n        while (j \u003C n) {\n          const ch = css[j];\n          if (ch === \"(\") depth++;\n          else if (ch === \")\") depth = Math.max(0, depth - 1);\n          else if (depth === 0 && (ch === \"{\" || ch === \";\" || ch === \"}\")) break;\n          j++;\n        }\n        const prelude = css.slice(start, j).trim();\n\n        if (j >= n) {\n          pushDecl(nodes, prelude);\n          i = j;\n          break;\n        }\n        if (css[j] === \";\") {\n          i = j + 1;\n          pushDecl(nodes, prelude);\n          continue;\n        }\n        if (css[j] === \"{\") {\n          i = j + 1;\n          const body = parseBlock(\"}\");\n          nodes.push({ type: \"rule\", selector: prelude, body });\n          continue;\n        }\n        \u002F\u002F css[j] === \"}\" — a trailing declaration with no semicolon before the brace\n        pushDecl(nodes, prelude);\n        i = j + 1;\n        break;\n      }\n      return nodes;\n    }\n\n    function pushDecl(nodes, prelude) {\n      if (!prelude) return;\n      const idx = prelude.indexOf(\":\");\n      if (idx > -1) {\n        nodes.push({ type: \"decl\", prop: prelude.slice(0, idx).trim(), value: prelude.slice(idx + 1).trim() });\n      }\n    }\n\n    return parseBlock(null);\n  }\n\n  \u002F\u002F ---------- & resolution ----------\n  function analyzeNested(raw) {\n    const t = raw.trim();\n    let invalid = false;\n    for (let i = 0; i \u003C t.length; i++) {\n      if (t[i] === \"&\") {\n        const next = t[i + 1];\n        if (next !== undefined && \u002F[A-Za-z0-9_-]\u002F.test(next)) { invalid = true; break; }\n      }\n    }\n    let kind;\n    if (invalid) kind = \"invalid\";\n    else if (\u002F^&::?\u002F.test(t)) kind = \"pseudo\";\n    else if (\u002F^&[.#[]\u002F.test(t)) kind = \"modifier\";\n    else if (\u002F^&\\s+\u002F.test(t)) kind = \"explicit-descendant\";\n    else if (t === \"&\") kind = \"bare-amp\";\n    else if (t.indexOf(\"&\") > -1) kind = \"other-amp\";\n    else kind = \"implicit-descendant\";\n    return { invalid, kind };\n  }\n\n  function resolveSelector(t, parent) {\n    if (t.indexOf(\"&\") > -1) return t.split(\"&\").join(parent).replace(\u002F\\s+\u002Fg, \" \").trim();\n    return (parent + \" \" + t).replace(\u002F\\s+\u002Fg, \" \").trim();\n  }\n\n  \u002F\u002F ---------- flatten nodes into printable \"compiled\" blocks ----------\n  function flattenNodes(nodes, parentList, out, mediaHeader) {\n    const effParent = parentList.length ? parentList : [\"\"];\n    let cur = [];\n    function flush() {\n      if (cur.length) {\n        out.push({ kind: parentList._kind || \"base\", selectors: effParent.slice(), decls: cur, mediaHeader: mediaHeader || null });\n        cur = [];\n      }\n    }\n    for (const node of nodes) {\n      if (node.type === \"decl\") {\n        cur.push({ prop: node.prop, value: node.value });\n      } else if (node.type === \"rule\") {\n        flush();\n        const nestedParts = node.selector.split(\",\").map((s) => s.trim()).filter(Boolean);\n        if (!nestedParts.length) continue;\n        const analyses = nestedParts.map(analyzeNested);\n        if (analyses.some((a) => a.invalid)) {\n          out.push({ kind: \"invalid\", raw: node.selector.trim(), mediaHeader: mediaHeader || null });\n          continue; \u002F\u002F the whole rule (and anything nested inside it) is dropped\n        }\n        const resolved = [];\n        for (const p of effParent) {\n          for (const part of nestedParts) resolved.push(resolveSelector(part, p));\n        }\n        resolved._kind = analyses[0].kind;\n        flattenNodes(node.body, resolved, out, mediaHeader);\n      } else if (node.type === \"atrule\") {\n        flush();\n        flattenNodes(node.body, parentList, out, node.header);\n      }\n    }\n    flush();\n  }\n\n  function flattenTop(nodes) {\n    const out = [];\n    for (const node of nodes) {\n      if (node.type === \"rule\") {\n        const parts = node.selector.split(\",\").map((s) => s.trim()).filter(Boolean);\n        if (!parts.length) continue;\n        parts._kind = \"base\";\n        flattenNodes(node.body, parts, out, null);\n      } else if (node.type === \"atrule\") {\n        flattenNodes(node.body, [], out, node.header);\n      }\n    }\n    return out;\n  }\n\n  \u002F\u002F ---------- rendering the compiled panel ----------\n  function escapeHtml(s) {\n    return String(s).replace(\u002F&\u002Fg, \"&\").replace(\u002F\u003C\u002Fg, \"<\").replace(\u002F>\u002Fg, \">\");\n  }\n  function tokenizeValue(value) {\n    let v = escapeHtml(value);\n    v = v.replace(\u002F(\"[^\"]*\"|'[^']*')\u002Fg, '\u003Cspan class=\"tok-str\">$1\u003C\u002Fspan>');\n    v = v.replace(\u002F\\b\\d+(\\.\\d+)?(px|rem|em|%|deg|s|ms)?\\b\u002Fg, '\u003Cspan class=\"tok-num\">$&\u003C\u002Fspan>');\n    return v;\n  }\n  function indent(str, spaces) {\n    const pad = \" \".repeat(spaces);\n    return str.split(\"\\n\").map((l) => pad + l).join(\"\\n\");\n  }\n\n  function formatCompiled(blocks) {\n    return blocks\n      .map((b) => {\n        const effKind = b.mediaHeader ? \"media\" : b.kind;\n        if (b.kind === \"invalid\") {\n          let body =\n            `\u003Cspan class=\"tok-cmt\">\u002F* ${escapeHtml(b.raw)} — invalid: & cannot be followed directly\\n   by a bare identifier. The browser drops this whole rule. *\u002F\u003C\u002Fspan>`;\n          if (b.mediaHeader) {\n            body = `\u003Cspan class=\"tok-kw\">${escapeHtml(b.mediaHeader)}\u003C\u002Fspan> {\\n${indent(body, 2)}\\n}`;\n          }\n          return `\u003Cdiv class=\"crule invalid\" data-kind=\"invalid\">${body}\u003C\u002Fdiv>`;\n        }\n        const selLine = b.selectors.map((s) => `\u003Cspan class=\"tok-sel\">${escapeHtml(s)}\u003C\u002Fspan>`).join(\",\\n\");\n        const declBlock = b.decls\n          .map((d) => `\u003Cspan class=\"tok-prop\">${escapeHtml(d.prop)}\u003C\u002Fspan>: ${tokenizeValue(d.value)};`)\n          .join(\"\\n\");\n        let rule = `${selLine} {\\n${indent(declBlock, 2)}\\n}`;\n        if (b.mediaHeader) {\n          rule = `\u003Cspan class=\"tok-kw\">${escapeHtml(b.mediaHeader)}\u003C\u002Fspan> {\\n${indent(rule, 2)}\\n}`;\n        }\n        return `\u003Cdiv class=\"crule\" data-kind=\"${effKind}\">${rule}\u003C\u002Fdiv>`;\n      })\n      .join(\"\");\n  }\n\n  function applyKindFilter() {\n    const rules = compiledEl.querySelectorAll(\".crule\");\n    rules.forEach((r) => {\n      const k = r.dataset.kind;\n      r.classList.remove(\"hl\", \"dim\");\n      if (currentKind === \"all\") return;\n      if (k === currentKind) r.classList.add(\"hl\");\n      else r.classList.add(\"dim\");\n    });\n  }\n\n  \u002F\u002F ---------- render pipeline ----------\n  function setParseStatus(ok) {\n    parseDot.className = \"dot \" + (ok ? \"good\" : \"warn\");\n    parseText.textContent = ok ? \"Parsed OK — updated live.\" : \"Couldn't parse that yet — showing the last valid version.\";\n  }\n\n  function updatePreview(raw) {\n    const doc = frame.contentDocument;\n    if (!doc) return;\n    const styleEl = doc.getElementById(\"dynamic\");\n    if (styleEl) styleEl.textContent = raw;\n  }\n\n  function render() {\n    const raw = srcEl.value;\n    let blocks;\n    try {\n      const nodes = parseCSS(stripComments(raw));\n      blocks = flattenTop(nodes);\n    } catch (e) {\n      setParseStatus(false);\n      return;\n    }\n    setParseStatus(true);\n    compiledEl.innerHTML = formatCompiled(blocks);\n    applyKindFilter();\n    updatePreview(raw);\n  }\n\n  \u002F\u002F ---------- wiring ----------\n  srcEl.addEventListener(\"input\", () => {\n    clearTimeout(debounceTimer);\n    debounceTimer = setTimeout(render, 120);\n  });\n\n  document.querySelectorAll(\"[data-preset]\").forEach((btn) => {\n    btn.addEventListener(\"click\", () => {\n      srcEl.value = btn.dataset.preset === \"mistake\" ? MISTAKE_CSS : DEFAULT_CSS;\n      clearTimeout(debounceTimer);\n      render();\n    });\n  });\n\n  kindSeg.addEventListener(\"click\", (e) => {\n    const btn = e.target.closest(\"button[data-kind]\");\n    if (!btn) return;\n    currentKind = btn.dataset.kind;\n    [...kindSeg.querySelectorAll(\"button\")].forEach((b) => b.setAttribute(\"aria-pressed\", String(b === btn)));\n    kindCaption.textContent = CAPTIONS[currentKind];\n    applyKindFilter();\n  });\n\n  viewportSeg.addEventListener(\"click\", (e) => {\n    const btn = e.target.closest(\"button[data-vp]\");\n    if (!btn) return;\n    [...viewportSeg.querySelectorAll(\"button\")].forEach((b) => b.setAttribute(\"aria-pressed\", String(b === btn)));\n    stageWrap.classList.toggle(\"narrow\", btn.dataset.vp === \"narrow\");\n  });\n\n  featuredToggle.addEventListener(\"change\", () => {\n    const doc = frame.contentDocument;\n    if (!doc) return;\n    const card = doc.querySelector(\".card\");\n    if (card) card.classList.toggle(\"card--featured\", featuredToggle.checked);\n  });\n\n  $(\"reset\").addEventListener(\"click\", () => {\n    clearTimeout(debounceTimer);\n    srcEl.value = DEFAULT_CSS;\n    currentKind = \"all\";\n    kindCaption.textContent = CAPTIONS.all;\n    [...kindSeg.querySelectorAll(\"button\")].forEach((b) => b.setAttribute(\"aria-pressed\", b.dataset.kind === \"all\" ? \"true\" : \"false\"));\n    [...viewportSeg.querySelectorAll(\"button\")].forEach((b) => b.setAttribute(\"aria-pressed\", b.dataset.vp === \"wide\" ? \"true\" : \"false\"));\n    stageWrap.classList.remove(\"narrow\");\n    featuredToggle.checked = false;\n    render();\n    const doc = frame.contentDocument;\n    if (doc) {\n      const card = doc.querySelector(\".card\");\n      if (card) card.classList.remove(\"card--featured\");\n    }\n  });\n\n  \u002F\u002F Feature check — the & nesting selector itself, via CSS.supports' selector() syntax.\n  (function checkSupport() {\n    const ok = window.CSS && CSS.supports && CSS.supports(\"selector(&)\");\n    if (!ok) {\n      supportBanner.textContent =\n        \"Your browser doesn't fully support the & nesting selector yet — the live preview and compiled panel below may not match what an up-to-date Chrome, Firefox, Safari, or Edge would show.\";\n      supportBanner.classList.add(\"show\");\n    }\n  })();\n\n  srcEl.value = DEFAULT_CSS;\n  frame.srcdoc = FRAME_HTML;\n  frame.addEventListener(\"load\", () => render(), { once: true });",{"height":11,"autorun":12},520,true,{"slug":4,"title":14,"excerpt":15,"coverUrl":16},"You kept Sass for one reason. Native CSS nesting just ended it.","CSS has supported nesting natively since 2023 — pseudo-classes, pseudo-elements, and @media queries nested inside the rules they belong to. No compiler required.","\u002Fmedia\u002Fcovers\u002Fcss-nesting-sass-replaced.png",[18,33],{"id":19,"slug":20,"name":21,"tagline":22,"description":23,"accentFrom":24,"accentTo":25,"icon":26,"defaultLocale":27,"locales":28,"features":30,"position":32},"019fe637-3d33-714b-b57f-23e163ffca0c","dev","Web Development","Build. Learn. Ship.","Practical courses, engineering-grade articles and open-source tools for people who ship.","violet-500","cyan-400","◇","en",[27,29],"fa",{"courses":12,"paths":12,"articles":12,"exams":31,"flashcards":31,"packages":12,"community":12,"certificates":12,"teams":12,"commerce":12},false,0,{"id":34,"slug":35,"name":36,"tagline":37,"description":38,"accentFrom":39,"accentTo":24,"icon":40,"defaultLocale":27,"locales":41,"features":43,"position":44},"019fe637-3dc2-754c-8657-0f175bfee7c6","lang","Languages","Learn a language the way you learn a codebase.","Structured paths, listening drills and spaced repetition that actually sticks.","amber-400","⌘",[27,29,42],"es",{"courses":12,"paths":12,"articles":31,"exams":31,"flashcards":31,"packages":31,"community":12,"certificates":31,"teams":31,"commerce":12},2]