/* ════════════════════════════════════════════════════════
   COMPONENT — BUTTONS
   The single button system used across the entire site:
   nav, filters, CTAs, back-to-top, dropdowns, etc. All
   variants share one base so spacing, radius, motion, and
   focus rings stay in lockstep when tokens change.

   Variants (combine with .btn):
   • .btn--primary  — filled accent, paper text. CTAs.
   • .btn--secondary — outlined; accent border. Quiet CTAs.
   • .btn--ghost    — text only with hairline underline.
                       For inline/in-text actions.
   • .btn--filter   — chip-style toggle for filter bars.
   • .btn--icon     — square, icon-only. Back-to-top, close.

   Sizes:
   • (default)      — 40px tall, comfortable tap target.
   • .btn--sm       — 32px tall, compact rows (filter bars).
   • .btn--lg       — 48px tall, hero CTAs.
   ════════════════════════════════════════════════════════ */

.btn {
  /* Layout */
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 10px;
  padding: 0 18px;
  height: 40px;
  min-width: 0;
  white-space: nowrap;

  /* Type */
  font-family: var(--display);
  font-weight: 600;
  font-variation-settings: "wdth" 96, "opsz" 14;
  font-size: var(--t-87);
  letter-spacing: -0.005em;
  line-height: 1;

  /* Surface */
  background: transparent;
  color: var(--ink);
  border: 1px solid transparent;
  border-radius: var(--radius-1);
  cursor: pointer;
  user-select: none;
  text-decoration: none;

  /* Motion */
  transition:
    background-color var(--dur-fast) var(--ease-out),
    color var(--dur-fast) var(--ease-out),
    border-color var(--dur-fast) var(--ease-out),
    transform var(--dur-fast) var(--ease-out),
    box-shadow var(--dur-base) var(--ease-out);
}

.btn:focus { outline: none; }
.btn:focus-visible {
  /* Two-ring focus indicator that reads on any background — the
     inset ring keeps the focus visible on light surfaces, the
     outer ring on dark/colored surfaces. */
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}
.btn:disabled,
.btn[aria-disabled="true"] {
  opacity: 0.4;
  pointer-events: none;
  cursor: not-allowed;
}

/* Size variants ─────────────────────────────────────────── */
.btn--sm {
  height: 32px;
  padding: 0 14px;
  font-size: var(--t-81);
  gap: 8px;
}
.btn--lg {
  height: 48px;
  padding: 0 24px;
  font-size: var(--t-94);
  gap: 12px;
}

/* PRIMARY — filled accent ────────────────────────────────── */
.btn--primary {
  background: var(--accent);
  color: var(--accent-ink);
  border-color: var(--accent);
}
.btn--primary:hover {
  background: var(--accent-quiet);
  border-color: var(--accent-quiet);
  transform: translateY(-1px);
  box-shadow: var(--shadow-1);
}
.btn--primary:active { transform: translateY(0); box-shadow: none; }

/* SECONDARY — outlined ───────────────────────────────────── */
.btn--secondary {
  background: var(--paper);
  color: var(--ink);
  border-color: color-mix(in srgb, var(--ink) 20%, transparent);
}
.btn--secondary:hover {
  border-color: var(--accent);
  color: var(--accent);
}
.btn--secondary:active { transform: translateY(1px); }

/* GHOST — text-only ───────────────────────────────────────── */
.btn--ghost {
  background: transparent;
  color: var(--ink);
  padding: 0 6px;
  border-color: transparent;
  position: relative;
}
.btn--ghost::after {
  content: '';
  position: absolute;
  left: 6px; right: 6px;
  bottom: 8px;
  height: 1px;
  background: currentColor;
  opacity: 0;
  transform: scaleX(0);
  transform-origin: left center;
  transition:
    opacity var(--dur-fast) var(--ease-out),
    transform var(--dur-mid) var(--ease-out);
}
.btn--ghost:hover { color: var(--accent); }
.btn--ghost:hover::after { opacity: 1; transform: scaleX(1); }

/* FILTER — chip-style toggle ─────────────────────────────── */
/* Used by sticky filter bars. Inactive: outlined ghost.
   Active (aria-pressed=true): filled accent. The aria-pressed
   attribute is the source of truth for active state — JS only
   toggles the attribute, CSS handles all the visual swap. */
.btn--filter {
  height: 36px;
  padding: 0 16px;
  font-size: var(--t-81);
  gap: 8px;
  background: var(--paper);
  color: var(--ink-soft);
  border-color: color-mix(in srgb, var(--ink) 14%, transparent);
  font-family: var(--display);
  font-weight: 600;
  letter-spacing: 0.005em;
  font-variation-settings: "wdth" 96, "opsz" 14;
  text-transform: none;
}
.btn--filter:hover {
  color: var(--ink);
  border-color: color-mix(in srgb, var(--ink) 28%, transparent);
}
.btn--filter[aria-pressed="true"] {
  background: var(--ink);
  color: var(--paper);
  border-color: var(--ink);
}
.btn--filter[aria-pressed="true"]:hover {
  background: color-mix(in srgb, var(--ink) 90%, var(--accent) 10%);
  border-color: color-mix(in srgb, var(--ink) 90%, var(--accent) 10%);
}
.btn--filter .count {
  font-family: var(--mono);
  font-size: var(--t-69);
  letter-spacing: 0.04em;
  opacity: 0.7;
  font-feature-settings: "tnum";
}
.btn--filter[aria-pressed="true"] .count { opacity: 0.85; }

/* ICON — square, icon-only ───────────────────────────────── */
.btn--icon {
  width: 40px;
  height: 40px;
  padding: 0;
  border-radius: var(--radius-2);
  background: var(--paper);
  border-color: color-mix(in srgb, var(--ink) 14%, transparent);
}
.btn--icon.btn--sm { width: 32px; height: 32px; }
.btn--icon.btn--lg { width: 48px; height: 48px; }
.btn--icon:hover {
  border-color: color-mix(in srgb, var(--ink) 28%, transparent);
  color: var(--accent);
}
.btn--icon svg {
  width: 18px;
  height: 18px;
  display: block;
}
.btn--icon.btn--sm svg { width: 14px; height: 14px; }

/* When a button-group needs a hairline divider — used by the
   sticky filter bar when filter buttons share a single track */
.btn-group {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  flex-wrap: wrap;
}

/* Reduced motion — kill transforms, keep color changes */
@media (prefers-reduced-motion: reduce) {
  .btn,
  .btn--ghost::after { transition: none; }
  .btn:hover { transform: none; }
}