/* Buttons – pill shaped, minimum 44 px tall.
   .btn            primary: inverse of the surface (graphite on light, white on graphite)
   .btn--secondary outlined
   .btn--link      text link with arrow
   .btn--on-photo  white pill for use over photos
   Sizes: .btn--lg (56 px), default (48 px), .btn--sm (44 px).
   States: :hover, :active, :focus-visible (LED ring), [aria-busy="true"] (spinner), [disabled].
   .is-hover / .is-active / .is-focus force a state for documentation only. */

.btn {
  --btn-bg: var(--fg);
  --btn-fg: var(--bg);
  --btn-bg-hover: color-mix(in srgb, var(--fg) 84%, var(--bg));
  --btn-border: transparent;
  --btn-h: 48px;
  --btn-px: 24px;
  --btn-font: 1rem;

  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.55em;
  min-height: var(--btn-h);
  padding: 0 var(--btn-px);
  border: 1px solid var(--btn-border);
  border-radius: var(--radius-pill);
  background: var(--btn-bg);
  color: var(--btn-fg);
  font: inherit;
  font-size: var(--btn-font);
  font-weight: 600;
  letter-spacing: -0.005em;
  line-height: 1;
  text-decoration: none;
  white-space: nowrap;
  cursor: pointer;
  -webkit-tap-highlight-color: transparent;
  transition:
    background-color var(--dur-fast) var(--ease-out),
    border-color var(--dur-fast) var(--ease-out),
    color var(--dur-fast) var(--ease-out),
    transform var(--dur-instant) var(--ease-out),
    box-shadow var(--dur-base) var(--ease-out);
}

.btn__icon {
  width: 1.1em;
  height: 1.1em;
  flex: none;
  transition: transform var(--dur-base) var(--ease-emphasis);
}

.btn:hover,
.btn.is-hover {
  background: var(--btn-bg-hover);
}

.btn:hover .btn__icon--forward,
.btn.is-hover .btn__icon--forward {
  transform: translateX(3px);
}

.btn:hover .btn__icon--down,
.btn.is-hover .btn__icon--down {
  transform: translateY(2px);
}

.btn:active,
.btn.is-active {
  transform: scale(0.98);
}

/* Keyboard focus: the LED edge as a ring */
.btn:focus-visible,
.btn.is-focus {
  outline: none;
  box-shadow: 0 0 0 2px var(--bg), 0 0 0 3.5px var(--accent), 0 0 16px 3px var(--accent-glow);
}

/* Secondary */
.btn--secondary {
  --btn-bg: transparent;
  --btn-fg: var(--fg);
  --btn-border: var(--line-strong);
  --btn-bg-hover: var(--bg-raised);
}

.surface-mist .btn--secondary {
  --btn-bg-hover: var(--white);
}

/* Text link */
.btn--link {
  --btn-bg: transparent;
  --btn-fg: var(--fg);
  --btn-bg-hover: transparent;
  --btn-px: 2px;
  min-height: 44px;
  border-radius: var(--radius-s);
  text-decoration: underline;
  text-decoration-color: transparent;
  text-underline-offset: 0.3em;
  text-decoration-thickness: 1.5px;
}

.btn--link:hover,
.btn--link.is-hover {
  text-decoration-color: currentColor;
}

/* Over photos */
.btn--on-photo {
  --btn-bg: #ffffff;
  --btn-fg: #16181b;
  --btn-bg-hover: rgb(255 255 255 / 0.86);
}

.btn--on-photo.btn--secondary {
  --btn-bg: rgb(255 255 255 / 0.12);
  --btn-fg: #ffffff;
  --btn-border: rgb(255 255 255 / 0.55);
  --btn-bg-hover: rgb(255 255 255 / 0.22);
  -webkit-backdrop-filter: blur(10px);
  backdrop-filter: blur(10px);
}

/* Sizes */
.btn--lg {
  --btn-h: 56px;
  --btn-px: 30px;
  --btn-font: 1.0625rem;
}

.btn--sm {
  --btn-h: 44px;
  --btn-px: 18px;
  --btn-font: 0.9375rem;
}

/* Loading */
.btn__spinner {
  display: none;
  width: 1em;
  height: 1em;
  flex: none;
  border: 2px solid currentColor;
  border-right-color: transparent;
  border-radius: 50%;
  animation: btn-spin 800ms linear infinite;
}

.btn[aria-busy="true"] {
  cursor: progress;
}

.btn[aria-busy="true"] .btn__spinner {
  display: inline-block;
}

.btn[aria-busy="true"] .btn__icon {
  display: none;
}

@keyframes btn-spin {
  to {
    transform: rotate(360deg);
  }
}

@media (prefers-reduced-motion: reduce) {
  .btn__spinner {
    animation: none;
    border-right-color: currentColor;
    opacity: 0.6;
  }
}

/* Done: swap the icon for a check mark */
.btn__icon--done {
  display: none;
}

.btn.is-done .btn__icon--done {
  display: inline-block;
}

.btn.is-done .btn__icon:not(.btn__icon--done) {
  display: none;
}

/* Unavailable */
.btn:disabled,
.btn[aria-disabled="true"] {
  --btn-bg: var(--line);
  --btn-fg: var(--fg-muted);
  --btn-bg-hover: var(--line);
  --btn-border: transparent;
  cursor: not-allowed;
  transform: none;
}

.btn--link:disabled,
.btn--link[aria-disabled="true"] {
  --btn-bg: transparent;
  --btn-bg-hover: transparent;
}