Glassmorphism (Frosted & Liquid Glass)

Translucent, frosted UI: panels you can see through, blurred so the backdrop reads as soft color, rimmed by a bright edge of light, floating on layered shadow. The 2026 "liquid glass" evolution adds refraction — the background visibly bends through the panel — plus moving specular highlights. The goal is depth and material, not just opacity.

When to use

• Frosted cards, nav bars, sidebars, modals/dialogs, and toolbars over busy/photo backgrounds
• Login/hero panels and overlays that should feel layered above the page
• Apple-style "liquid glass" heroes: refracting, slowly churning surfaces with a specular sweep
• Hover/scroll/enter motion on glass — frost deepening, highlight brightening, the panel lifting
• Any place where content needs to read as floating glass while staying legible

The four ingredients of believable glass

Glass is never one property. Every panel needs all four, or it reads as a plain translucent box:

1. Frost — backdrop-filter: blur() plus saturate() to keep backdrop color vivid through the blur.
2. Translucency — a background with alpha (~0.08–0.18), never fully opaque, never fully clear.
3. Edge of glass — a hairline border brighter than the fill, ideally a lit top-left → dim bottom-right highlight, so the rim catches light.
4. Depth — layered box-shadow: an ambient drop shadow to float it, plus an inset top highlight and bottom shade to round the surface.

.glass {
  background: rgba(255, 255, 255, 0.12);
  backdrop-filter: blur(16px) saturate(160%);
  -webkit-backdrop-filter: blur(16px) saturate(160%); /* Safari needs the prefix */
  border-radius: 20px;
  border: 1px solid rgba(255, 255, 255, 0.25);
  box-shadow:
    0 8px 32px rgba(0, 0, 0, 0.25),     /* float */
    inset 0 1px 0 rgba(255, 255, 255, 0.35), /* top highlight */
    inset 0 -1px 0 rgba(0, 0, 0, 0.12);      /* bottom shade */
}

Frost tiers: light UI chrome blur(8–12px) / alpha 0.08–0.14; heavy modal/login blur(24–40px) / alpha 0.10–0.18. Dark glass: fill rgba(0,0,0,0.3), softer top highlight.

backdrop-filter only blurs content that sits behind the element. Over a flat background color it does nothing visible — glass needs a busy backdrop (image, gradient, video) to frost.

Specular edge highlight and anti-banding grain

A flat border is dead. Draw a masked 1px ring with a lit corner via ::before, and dither away gradient banding (stepped contour lines under heavy blur) with a faint feTurbulence noise overlay via ::after at opacity ≤ 0.06. Full masked-border and inline-noise recipes are in references/glass-recipes.md.

Motion: animate the glass, not the geometry

Animate the qualities of the glass — frost deepening, highlight brightening, the panel lifting — so it reads as the surface "leaning into the light."

.glass {
  transition: backdrop-filter .4s ease, background .4s ease,
              box-shadow .4s ease, transform .4s cubic-bezier(.16,1,.3,1);
}
.glass:hover {
  backdrop-filter: blur(24px) saturate(180%);
  background: rgba(255,255,255,.18);
  transform: translateY(-4px);
  box-shadow: 0 16px 48px rgba(0,0,0,.3), inset 0 1px 0 rgba(255,255,255,.5);
}

• Entrance (frost resolving from clear): pair a [data-enter] transition with @starting-style { backdrop-filter: blur(0); opacity: 0; transform: translateY(16px) }.
• Specular sweep: a skewed white gradient animated across the surface on hover or as a slow ambient loop.
• Caveat: animating the blur radius is the most expensive thing here — the backdrop is re-blurred every frame. If hover janks, animate transform/box-shadow/background (cheap) and keep the blur delta small or snap it.

Liquid glass — SVG refraction (the 2026 look)

Bend the background through the panel like a thick lens: drive feDisplacementMap from animated feTurbulence, applied via filter (it distorts the element's own pixels) layered over a backdrop-filter frost.

<svg width="0" height="0" style="position:absolute"><filter id="liquid-glass">
  <feTurbulence type="fractalNoise" baseFrequency="0.008 0.012" numOctaves="2" seed="3" result="n">
    <animate attributeName="baseFrequency" dur="18s"
             values="0.008 0.012;0.012 0.008;0.008 0.012" repeatCount="indefinite"/>
  </feTurbulence>
  <feDisplacementMap in="SourceGraphic" in2="n" scale="22" xChannelSelector="R" yChannelSelector="G"/>
</filter></svg>

scale = refraction strength (8–14 subtle, 20–30 pronounced, >40 molten). Lower baseFrequency = larger, slower waves (more liquid). Keep the animate dur long (12–20s) so it breathes. These filters are heavy — use on one hero element, not a grid.

Performance — backdrop-filter is expensive

• Each glass element re-samples and blurs everything behind it. Limit the count; a dozen on screen tanks scroll FPS.
• Promote heavy glass to its own layer (transform: translateZ(0) or will-change: transform), and remove will-change after the animation.
• Don't stack backdrop-filter elements over each other — nested blur re-blurs the blur (quadratic cost).
• Big radii (>40px) over large areas are the worst case; cap radius and panel size.

Accessibility — non-negotiable

Glass is decoration; content must stay legible and the effect must be defeatable.

@media (prefers-reduced-transparency: reduce) {
  .glass { background: #1a1a2e; backdrop-filter: none; -webkit-backdrop-filter: none; }
  .glass::after { display: none; }            /* drop grain */
}
@media (prefers-reduced-motion: reduce) {
  .glass { transition: none; }
  .liquid { filter: none; }                   /* stop the refraction churn */
}
@supports not (backdrop-filter: blur(1px)) {
  .glass { background: rgba(30,30,50,.85); }  /* opaque-enough fallback */
}

Contrast over busy backgrounds: translucent panels over photos can drop text below WCAG. Add a semi-opaque scrim or darkening gradient under the text, optionally text-shadow: 0 1px 2px rgba(0,0,0,.4), and verify ≥ 4.5:1 body / ≥ 3:1 large against the brightest region of the backdrop.

Deliver & verify (standalone HTML)

Packaged helper (scripts/): scripts/seek-shot.sh anim.html 0 1.5 3 freezes the ?t=N harness and screenshots each moment; scripts/contact-sheet.sh sheet.png frame-*.png tiles them for one-glance review. See scripts/README.md.

For a self-contained glass demo (card, nav, modal, liquid-glass hero) the deliverable is one HTML file that opens directly in a browser — markup, CSS, and (if liquid) one inline SVG filter, no build step. A single file is the right tier for a glass surface; don't reach for a bundler. The panel must overlap a real backdrop (drop in a photo or gradient) or there is nothing to frost and the demo lies.

Output contract:

• One .html file: a busy backdrop, your glass markup, the CSS (frost + edge highlight + grain + shadows), and any inline SVG feDisplacementMap filter.
• A way to land on the resolved state and a frozen frame of any loop — glass verifies by both state (rest/hover/enter) and time (the sweep/refraction).
• Include the freeze harness below so any moment can be pinned for inspection.

Seek harness — pin a deterministic state + frame. ?state=hover forces the hover look; ?t=N freezes CSS animations and the SVG refraction at N seconds, so a screenshot lands on a still, deterministic frame:

<script>
  const p = new URLSearchParams(location.search);
  const state = p.get("state");
  if (state) document.documentElement.dataset.state = state;   // CSS keys off :root[data-state="hover"]
  const t = p.get("t");
  if (t !== null) {
    document.getAnimations().forEach(a => { a.currentTime = parseFloat(t)*1000; a.pause(); }); // freeze CSS sweep
    const svg = document.querySelector("svg");
    svg?.pauseAnimations?.(); svg?.setCurrentTime?.(parseFloat(t));                            // freeze refraction
  }
  window.__ready = true;
</script>

Verify loop — render → set state/freeze → screenshot → check: open each meaningful state (?state=rest, ?state=hover) and a frozen loop frame (?t=2), screenshot, and confirm the glass reads as glass — blur and edge highlight visibly present, no color banding, text contrast holds over the backdrop — plus check artifacts (flat box because the backdrop is plain color, missing -webkit- prefix in Safari, refraction too strong/molten, jank from animating blur). Then load prefers-reduced-transparency and confirm the solid fallback renders legibly. Any headless tool works:

npx playwright screenshot --wait-for-timeout=500 "file://$PWD/glass.html?state=hover" hover.png
npx playwright screenshot --wait-for-timeout=500 "file://$PWD/glass.html?t=2"          loop.png

To check the fallback headlessly, emulate the media feature (e.g. Playwright --color-scheme-style flags, or a ?reduced=1 query that toggles a class mirroring the media query) and screenshot that the panel is solid and readable.

Before you finish:

1. Opens standalone — no console errors; the glass overlaps a real busy backdrop, not a flat color.
2. Reads as glass — blur + bright edge highlight both visible, layered shadow floats it, no banding (grain present).
3. Text contrast holds over the brightest part of the backdrop (≥ 4.5:1 body).
4. ?state= / ?t=N freeze lands a deterministic, settled frame.
5. prefers-reduced-transparency → solid opaque panel; prefers-reduced-motion → refraction/sweep stopped; @supports fallback for no backdrop-filter.
6. Performance sane — glass count limited, blur not animated on a janky path, liquid refraction on one element only.

Quick reference

Reference files

• references/glass-recipes.md — full copy-paste recipes: base glass card with tiers, the masked specular edge ring, anti-banding grain, hover/enter/scroll motion, the specular sweep, the SVG feDisplacementMap/feTurbulence liquid-glass filter with tuning knobs, performance rules, the reduced-transparency/reduced-motion/@supports fallbacks, contrast defenses, and the standalone freeze harness.