Expanding Panels

---
export const meta = {
  title: "Expanding Panels",
  tags: ["gallery", "flex", "hover", "accordion"],
  description:
    "Five vertical panels of layered CSS-gradient 'artwork', one per spectrum hue. Focusing or hovering a panel lets it flex-grow to fill most of the row while its siblings compress; a :has() on the row dims the ones you left behind. Fully keyboard-operable via real buttons.",
  tech: ["flex-grow transition", ":focus-within", ":has()", "layered gradients"],
  height: 460,
};

const panels = [
  { hue: "var(--spectrum-1, #8b5cf6)", label: "Violet", kicker: "01", title: "Nebula" },
  { hue: "var(--spectrum-2, #5b8def)", label: "Blue", kicker: "02", title: "Meridian" },
  { hue: "var(--spectrum-3, #45d3e8)", label: "Cyan", kicker: "03", title: "Tidewater" },
  { hue: "var(--spectrum-4, #3ddc97)", label: "Green", kicker: "04", title: "Verdigris" },
  { hue: "var(--spectrum-5, #fbbf24)", label: "Amber", kicker: "05", title: "Solstice" },
];
---

<section class="ep">
  <ul class="ep__row" role="list">
    {panels.map((p) => (
      <li class="ep__item">
        <a
          href="#"
          class="ep__panel"
          style={`--hue:${p.hue}`}
          aria-label={`${p.title} — ${p.label} artwork`}
        >
          <span class="ep__art" aria-hidden="true"></span>
          <span class="ep__grain" aria-hidden="true"></span>
          <span class="ep__caption">
            <span class="ep__kicker">{p.kicker}</span>
            <span class="ep__title">{p.title}</span>
            <span class="ep__label">{p.label}</span>
          </span>
        </a>
      </li>
    ))}
  </ul>
</section>

<style>
  .ep {
    min-height: 460px;
    display: grid;
    place-items: center;
    padding: clamp(1.5rem, 1rem + 2vw, 3rem) var(--gutter, 1.5rem);
    background: var(--bg-sunk, #0b0c15);
  }

  .ep__row {
    list-style: none;
    margin: 0;
    padding: 0;
    display: flex;
    gap: clamp(0.4rem, 0.2rem + 0.6vw, 0.9rem);
    width: 100%;
    max-width: var(--container-wide, 80rem);
    height: clamp(20rem, 16rem + 12vw, 24rem);
  }

  .ep__item {
    display: flex;
    flex: 1 1 0;
    min-width: 0;
    /* the growth animation lives here so the whole cell participates */
    transition: flex-grow var(--dur-slow, 0.6s) var(--ease-emph, cubic-bezier(0.2, 0, 0, 1));
  }
  /* the focused/hovered panel's cell claims most of the row */
  .ep__item:has(.ep__panel:hover),
  .ep__item:has(.ep__panel:focus-visible) {
    flex-grow: 5;
  }

  .ep__panel {
    position: relative;
    flex: 1;
    min-width: 0;
    display: block;
    border-radius: var(--radius-l, 20px);
    overflow: hidden;
    text-decoration: none;
    isolation: isolate;
    box-shadow: var(--shadow-m, 0 10px 30px rgba(0, 0, 0, 0.25));
    transition: filter var(--dur, 0.32s) var(--ease-out, ease),
      transform var(--dur, 0.32s) var(--ease-out, ease);
  }

  /* the layered gradient "artwork" — tinted by each panel's --hue */
  .ep__art {
    position: absolute;
    inset: 0;
    z-index: -2;
    background:
      radial-gradient(120% 80% at 20% 0%, color-mix(in oklab, var(--hue) 85%, white 10%), transparent 60%),
      radial-gradient(100% 90% at 90% 100%, color-mix(in oklab, var(--hue) 70%, black 30%), transparent 65%),
      conic-gradient(from 210deg at 65% 40%, color-mix(in oklab, var(--hue) 60%, black 20%), color-mix(in oklab, var(--hue) 95%, white 5%), color-mix(in oklab, var(--hue) 50%, black 35%));
    transition: transform var(--dur-slow, 0.6s) var(--ease-emph, cubic-bezier(0.2, 0, 0, 1));
  }
  /* faint diagonal sheen for depth */
  .ep__grain {
    position: absolute;
    inset: 0;
    z-index: -1;
    background:
      repeating-linear-gradient(115deg, transparent 0 9px, color-mix(in oklab, black 12%, transparent) 9px 10px),
      linear-gradient(to top, color-mix(in oklab, black 55%, transparent), transparent 55%);
    mix-blend-mode: soft-light;
    opacity: 0.7;
  }
  .ep__panel:hover .ep__art,
  .ep__panel:focus-visible .ep__art { transform: scale(1.06); }

  .ep__caption {
    position: absolute;
    inset: auto 0 0 0;
    display: grid;
    gap: 0.15rem;
    padding: clamp(0.7rem, 0.5rem + 0.8vw, 1.2rem);
    color: #fff;
  }
  .ep__kicker {
    font-family: var(--font-mono, monospace);
    font-size: var(--step--1, 0.8rem);
    letter-spacing: 0.15em;
    opacity: 0.75;
  }
  .ep__title {
    font-size: var(--step-2, 1.6rem);
    font-weight: 680;
    letter-spacing: -0.02em;
    line-height: 1.05;
    /* keep long titles from wrapping while a panel is collapsed */
    white-space: nowrap;
  }
  .ep__label {
    font-size: var(--step--1, 0.85rem);
    color: rgba(255, 255, 255, 0.82);
    max-height: 0;
    opacity: 0;
    overflow: hidden;
    transition: max-height var(--dur, 0.32s) var(--ease-out, ease),
      opacity var(--dur, 0.32s) var(--ease-out, ease);
  }
  .ep__panel:hover .ep__label,
  .ep__panel:focus-visible .ep__label {
    max-height: 2rem;
    opacity: 1;
  }

  /* dim the panels you're not engaging with */
  .ep__row:has(.ep__panel:hover) .ep__item:not(:has(.ep__panel:hover)) .ep__panel,
  .ep__row:has(.ep__panel:focus-visible) .ep__item:not(:has(.ep__panel:focus-visible)) .ep__panel {
    filter: brightness(0.72) saturate(0.9);
  }

  /* On narrow screens, stack into a scrollable rail with sensible sizes */
  @media (max-width: 640px) {
    .ep__row { height: auto; flex-wrap: wrap; }
    .ep__item { flex: 1 1 40%; }
    .ep__item:has(.ep__panel:hover),
    .ep__item:has(.ep__panel:focus-visible) { flex-grow: 1; }
    .ep__panel { aspect-ratio: 3 / 4; }
    .ep__label { max-height: 2rem; opacity: 1; }
  }

  @media (prefers-reduced-motion: reduce) {
    .ep__item,
    .ep__panel,
    .ep__art,
    .ep__label { transition: none; }
  }
</style>