[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"verticals":3,"playground-css-scroll-state-container-queries":44,"search-suggestions":58},[4,20,32],{"id":5,"slug":6,"name":7,"tagline":8,"description":9,"accentFrom":10,"accentTo":11,"icon":12,"defaultLocale":13,"locales":14,"features":16,"position":19},"019fe637-3d33-714b-b57f-23e163ffca0c","dev","Web Development","Read it. Run it. Prove it.","A post a day on modern web development — most with an editable playground and a quiz that explains every answer. Free, no account needed.","violet-500","cyan-400","◇","en",[13,15],"fa",{"courses":17,"paths":17,"articles":17,"exams":18,"flashcards":18,"packages":17,"community":17,"certificates":17,"teams":17,"commerce":17},true,false,0,{"id":21,"slug":22,"name":23,"tagline":24,"description":25,"accentFrom":26,"accentTo":10,"icon":27,"defaultLocale":13,"locales":28,"features":30,"position":31},"019fe637-3dc2-754c-8657-0f175bfee7c6","lang","Languages","Learn a language the way you learn a codebase.","Grammar explained the way good documentation explains an API — one idea at a time, each with a quiz.","amber-400","⌘",[13,15,29],"es",{"courses":18,"paths":18,"articles":17,"exams":18,"flashcards":17,"packages":18,"community":17,"certificates":17,"teams":18,"commerce":18},2,{"id":33,"slug":34,"name":35,"tagline":36,"description":37,"accentFrom":38,"accentTo":39,"icon":40,"defaultLocale":13,"locales":41,"features":42,"position":43},"7b3c16f2-931d-410e-802e-e1fa4edab7de","soft","Soft Skills","The half of the job nobody wrote documentation for.","Weekly, on the parts of working life that decide more than your code does — first weeks, meetings, interviews, promotions, and the people around you. Written from what actually happens, and recorded as a podcast you can listen to on the walk.","emerald-400","teal-300","◉",[13],{"courses":18,"paths":18,"articles":17,"exams":18,"flashcards":18,"packages":18,"community":17,"certificates":18,"teams":18,"commerce":18},3,{"slug":45,"title":46,"summary":47,"html":48,"css":49,"js":50,"config":51,"doc":53},"css-scroll-state-container-queries","Is the header actually stuck? — scroll-state() vs IntersectionObserver",null,"\u003Cdiv class=\"pg\">\n    \u003Ch1 class=\"pg-title\">🎮 Is the header actually stuck?\u003C\u002Fh1>\n    \u003Cp class=\"pg-sub\">\n      Drag the banner slider, pick a detection method, then scroll the box below.\n      Watch \u003Cem>when\u003C\u002Fem> the header grows a shadow — and whether that moment still\n      matches reality once the layout above it changes.\n    \u003C\u002Fp>\n\n    \u003Cdiv class=\"panel\">\n      \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">1\u003C\u002Fspan> Controls\u003C\u002Fdiv>\n      \u003Cdiv class=\"seg\" id=\"modeSeg\" role=\"group\" aria-label=\"Detection method\">\n        \u003Cbutton type=\"button\" aria-pressed=\"true\" data-mode=\"css\">\u003Ccode>scroll-state()\u003C\u002Fcode> (new way)\u003C\u002Fbutton>\n        \u003Cbutton type=\"button\" aria-pressed=\"false\" data-mode=\"js\">IntersectionObserver (old way)\u003C\u002Fbutton>\n      \u003C\u002Fdiv>\n      \u003Cdiv class=\"field\" style=\"margin-top: 14px\">\n        \u003Clabel class=\"label\" for=\"bannerH\">Announcement banner height: \u003Cstrong id=\"bannerHVal\">64\u003C\u002Fstrong>px\u003C\u002Flabel>\n        \u003Cinput type=\"range\" id=\"bannerH\" min=\"16\" max=\"96\" step=\"8\" value=\"64\" \u002F>\n      \u003C\u002Fdiv>\n      \u003Cp class=\"hint\" id=\"modeHint\">\u003C\u002Fp>\n    \u003C\u002Fdiv>\n\n    \u003Cdiv class=\"panel\">\n      \u003Cdiv class=\"panel-label\">\u003Cspan class=\"n\">2\u003C\u002Fspan> Result — scroll inside the box\u003C\u002Fdiv>\n      \u003Cdiv class=\"demo-scroll\" id=\"scrollBox\">\n        \u003Cdiv class=\"demo-banner\" id=\"demoBanner\">📣 Free shipping this week\u003C\u002Fdiv>\n        \u003Cdiv class=\"intro\">Scroll down — the product header below locks to the top once it passes under the banner.\u003C\u002Fdiv>\n        \u003Cdiv class=\"sticky-wrap\" id=\"stickyWrap\">\n          \u003Cdiv class=\"sticky-header\" id=\"stickyHeader\">\n            \u003Cstrong>Wireless headphones\u003C\u002Fstrong>\n            \u003Cspan class=\"price\">$42\u003C\u002Fspan>\n          \u003C\u002Fdiv>\n        \u003C\u002Fdiv>\n        \u003Cdiv class=\"filler\">\n          \u003Cp>Product description, specs, reviews — the usual page filling the scroll space beneath a sticky add-to-cart bar.\u003C\u002Fp>\n          \u003Cp>Keep scrolling. The header above should only gain a drop shadow once it is genuinely pinned under the banner, not a moment before.\u003C\u002Fp>\n          \u003Cp>Scroll back up and the shadow should disappear the instant it unsticks, too.\u003C\u002Fp>\n        \u003C\u002Fdiv>\n      \u003C\u002Fdiv>\n\n      \u003Cdiv class=\"status\" id=\"status\" style=\"margin-top: 12px\">\n        \u003Cspan class=\"dot\" id=\"statusDot\">\u003C\u002Fspan>\u003Cspan id=\"statusText\">Scroll to begin.\u003C\u002Fspan>\n      \u003C\u002Fdiv>\n      \u003Cdiv class=\"readout output\" id=\"readout\" style=\"margin-top: 10px\">\u003C\u002Fdiv>\n      \u003Cp class=\"hint\" id=\"supportHint\">\u003C\u002Fp>\n    \u003C\u002Fdiv>\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.demo-scroll {\n    position: relative;\n    height: 300px;\n    overflow-y: auto;\n    border: 1px solid var(--line);\n    border-radius: var(--radius-sm);\n    background: var(--panel-2);\n  }\n  .demo-banner {\n    position: sticky;\n    top: 0;\n    z-index: 3;\n    display: flex;\n    align-items: center;\n    justify-content: center;\n    background: var(--accent);\n    color: var(--accent-ink);\n    font-size: 0.78rem;\n    font-weight: 800;\n    letter-spacing: 0.01em;\n    overflow: hidden;\n    transition: height 0.12s ease;\n  }\n  .intro, .filler {\n    padding: 16px 18px;\n    color: var(--muted);\n    font-size: 0.86rem;\n    line-height: 1.6;\n  }\n  .filler p { margin: 0 0 140px; }\n  .filler p:last-child { margin-bottom: 20px; }\n  .sticky-wrap {\n    position: sticky;\n    z-index: 2;\n    container-type: scroll-state;\n  }\n  .sticky-header {\n    display: flex;\n    align-items: center;\n    justify-content: space-between;\n    gap: 10px;\n    padding: 12px 16px;\n    background: var(--panel);\n    border-bottom: 1px solid var(--line);\n    transition: box-shadow 0.12s ease;\n  }\n  .sticky-header .price { color: var(--accent); font-weight: 800; }\n\n  \u002F* --- the CSS-only path: only active while #scrollBox carries .use-css --- *\u002F\n  .use-css .sticky-header {\n    \u002F* nothing by default — the shadow only appears once the container is\n       actually stuck, read straight from the browser's own state *\u002F\n  }\n  @container scroll-state(stuck: top) {\n    .use-css .sticky-header { box-shadow: 0 8px 16px rgba(0, 0, 0, 0.35); }\n  }\n\n  \u002F* --- the old way: a JS-toggled class, see the script below --- *\u002F\n  .sticky-header.js-shadow { box-shadow: 0 8px 16px rgba(0, 0, 0, 0.35); }\n\n  .readout { display: grid; gap: 6px; font-size: 0.86rem; }\n  .readout b { color: var(--ink); }\n  .mismatch { color: var(--bad); font-weight: 700; }\n  .ok { color: var(--good); font-weight: 700; }","\"use strict\";\nconst $ = (id) => document.getElementById(id);\nconst scrollBox = $(\"scrollBox\");\nconst demoBanner = $(\"demoBanner\");\nconst stickyWrap = $(\"stickyWrap\");\nconst stickyHeader = $(\"stickyHeader\");\nconst bannerSlider = $(\"bannerH\");\nconst bannerHVal = $(\"bannerHVal\");\nconst modeSeg = $(\"modeSeg\");\n\nconst HARDCODED_OFFSET = 64; \u002F\u002F the \"old way\": a rootMargin baked in the day it shipped\nlet mode = \"css\";\nlet sentinel = null;\nlet observer = null;\n\nconst supportsScrollState =\n  typeof CSS !== \"undefined\" && CSS.supports && CSS.supports(\"container-type\", \"scroll-state\");\n\nfunction setBannerHeight(px) {\n  demoBanner.style.height = px + \"px\";\n  stickyWrap.style.top = px + \"px\";\n  bannerHVal.textContent = px;\n}\n\nfunction setStatus(text, kind) {\n  $(\"statusText\").textContent = text;\n  $(\"statusDot\").className = \"dot \" + kind;\n}\n\nfunction teardownObserver() {\n  if (observer) { observer.disconnect(); observer = null; }\n  if (sentinel) { sentinel.remove(); sentinel = null; }\n  stickyHeader.classList.remove(\"js-shadow\");\n}\n\nfunction setupObserver() {\n  teardownObserver();\n  sentinel = document.createElement(\"div\");\n  sentinel.style.cssText = \"height:1px;\";\n  stickyWrap.before(sentinel);\n  observer = new IntersectionObserver(\n    ([entry]) => stickyHeader.classList.toggle(\"js-shadow\", !entry.isIntersecting),\n    { root: scrollBox, threshold: 0, rootMargin: `-${HARDCODED_OFFSET + 1}px 0px 0px 0px` }\n  );\n  observer.observe(sentinel);\n}\n\nfunction applyMode(next) {\n  mode = next;\n  [...modeSeg.querySelectorAll(\"button\")].forEach((b) =>\n    b.setAttribute(\"aria-pressed\", String(b.dataset.mode === next))\n  );\n  scrollBox.classList.toggle(\"use-css\", next === \"css\");\n\n  if (next === \"js\") {\n    setupObserver();\n    $(\"modeHint\").innerHTML =\n      \"This is the classic sentinel + \u003Ccode>IntersectionObserver\u003C\u002Fcode> trick. Its trigger point is hardcoded at \" +\n      `\u003Cstrong>${HARDCODED_OFFSET}px\u003C\u002Fstrong> — move the slider away from 64 and watch it drift out of sync.`;\n  } else {\n    teardownObserver();\n    $(\"modeHint\").innerHTML = supportsScrollState\n      ? \"\u003Ccode>container-type: scroll-state\u003C\u002Fcode> + \u003Ccode>@container scroll-state(stuck: top)\u003C\u002Fcode> read the browser's own state — the shadow always matches \u003Ccode>top\u003C\u002Fcode> exactly, whatever the slider is set to.\"\n      : \"Your browser doesn't support \u003Ccode>scroll-state()\u003C\u002Fcode> yet, so this mode will stay visually silent here — switch to the old way to see it actually work. Firefox and Safari don't ship this yet.\";\n  }\n  updateReadout();\n}\n\nfunction updateReadout() {\n  const headerRect = stickyHeader.getBoundingClientRect();\n  const boxRect = scrollBox.getBoundingClientRect();\n  const bannerPx = parseInt(bannerSlider.value, 10);\n  const actuallyStuck = headerRect.top \u003C= boxRect.top + bannerPx + 1;\n  const shadowShowing = getComputedStyle(stickyHeader).boxShadow !== \"none\";\n  const matches = actuallyStuck === shadowShowing;\n\n  setStatus(\n    actuallyStuck ? \"Header is genuinely stuck right now\" : \"Header is not stuck yet\",\n    actuallyStuck ? \"good\" : \"info\"\n  );\n\n  const lines = [\n    `Real stuck state: \u003Cb>${actuallyStuck ? \"stuck\" : \"not stuck\"}\u003C\u002Fb> (measured from the header's actual position)`,\n    `Shadow currently shown: \u003Cb>${shadowShowing ? \"yes\" : \"no\"}\u003C\u002Fb>`,\n  ];\n  if (mode === \"js\") {\n    const drift = bannerPx - HARDCODED_OFFSET;\n    lines.push(\n      drift === 0\n        ? `\u003Cspan class=\"ok\">✓ Hardcoded 64px happens to match the real banner height — no drift today.\u003C\u002Fspan>`\n        : `\u003Cspan class=\"mismatch\">✗ Hardcoded trigger (64px) vs real banner height (${bannerPx}px): off by ${Math.abs(drift)}px — the shadow toggles at the wrong scroll position.\u003C\u002Fspan>`\n    );\n  } else {\n    lines.push(\n      matches\n        ? `\u003Cspan class=\"ok\">✓ Shadow tracks the real stuck state exactly — nothing to recompute when the banner resizes.\u003C\u002Fspan>`\n        : supportsScrollState\n          ? `\u003Cspan class=\"mismatch\">Momentary mismatch — scroll events can lag a frame; this clears on the next scroll tick.\u003C\u002Fspan>`\n          : `\u003Cspan class=\"mismatch\">No native support detected, so this mode can't show a shadow in your browser.\u003C\u002Fspan>`\n    );\n  }\n  $(\"readout\").innerHTML = lines.map((l) => `\u003Cdiv>${l}\u003C\u002Fdiv>`).join(\"\");\n}\n\nbannerSlider.addEventListener(\"input\", () => {\n  setBannerHeight(parseInt(bannerSlider.value, 10));\n  updateReadout();\n});\n\nmodeSeg.addEventListener(\"click\", (e) => {\n  const btn = e.target.closest(\"button[data-mode]\");\n  if (btn) applyMode(btn.dataset.mode);\n});\n\nscrollBox.addEventListener(\"scroll\", () => requestAnimationFrame(updateReadout));\n\n$(\"supportHint\").innerHTML = supportsScrollState\n  ? \"✅ Your browser supports \u003Ccode>container-type: scroll-state\u003C\u002Fcode> natively — the new-way mode above is really running, not simulated.\"\n  : \"⚠️ Your browser reports no support for \u003Ccode>container-type: scroll-state\u003C\u002Fcode> (Chrome\u002FEdge 133+ only, as of this writing). The old-way mode still runs for real either way.\";\n\nsetBannerHeight(64);\napplyMode(\"css\");",{"height":52,"autorun":17},520,{"slug":45,"title":54,"excerpt":55,"coverUrl":56,"vertical":57},"Stop Writing JS to Detect a Stuck Header. `scroll-state()` Fixes It.","A sticky header that should only cast a shadow once it's actually stuck to the top usually means a hidden sentinel div and an IntersectionObserver. CSS now tracks that state itself — the `scroll-state()` container query reads it directly, no sentinel, no observer, no JS math.","\u002Fmedia\u002Fcovers\u002Fcss-scroll-state-container-queries.png",{"slug":6},[59,63,67,71,75,79,83,87,91,95,99,103],{"slug":60,"name":61,"articles":62},"webdev","Webdev",156,{"slug":64,"name":65,"articles":66},"javascript","Javascript",128,{"slug":68,"name":69,"articles":70},"frontend","Frontend",89,{"slug":72,"name":73,"articles":74},"tutorial","Tutorial",61,{"slug":76,"name":77,"articles":78},"css","Css",46,{"slug":80,"name":81,"articles":82},"performance","Performance",26,{"slug":84,"name":85,"articles":86},"typescript","Typescript",22,{"slug":88,"name":89,"articles":90},"react","React",19,{"slug":92,"name":93,"articles":94},"browser","Browser",15,{"slug":96,"name":97,"articles":98},"programming","Programming",14,{"slug":100,"name":101,"articles":102},"node","Node",13,{"slug":104,"name":105,"articles":106},"accessibility","Accessibility",10]