/* ==========================================================================
   button.css — primary / secondary / ghost, all states
   Square by design. DESIGN.md §9 #3.
   ========================================================================== */

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  min-height: 2.75rem;              /* 44px tap target */
  padding-block: var(--space-3);
  padding-inline: var(--space-5);

  font-size: var(--fs-xs);
  font-weight: var(--fw-medium);
  line-height: var(--lh-flat);
  letter-spacing: var(--ls-button);
  text-align: center;
  text-decoration: none;
  white-space: nowrap;

  border: var(--border-w) solid transparent;
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition:
    background-color var(--dur-fast) var(--ease),
    border-color var(--dur-fast) var(--ease),
    color var(--dur-fast) var(--ease),
    transform var(--dur-fast) var(--ease);
}

/* --- Primary ------------------------------------------------------------- */

.btn--primary {
  background-color: var(--accent);
  color: var(--on-accent);           /* 11.19:1 on --accent — verified       */
  border-color: var(--accent);
}

.btn--primary:hover {
  background-color: var(--accent-ink);
  color: var(--on-accent);           /* 15.75:1 on --accent-ink              */
  border-color: var(--accent-ink);
}

/* --- Secondary ----------------------------------------------------------- */

.btn--secondary {
  background-color: transparent;
  color: var(--text);
  border-color: var(--rule);
}

.btn--secondary:hover {
  background-color: var(--surface);
  color: var(--text);
  border-color: var(--border-strong);
}

/* --- Ghost --------------------------------------------------------------- */

.btn--ghost {
  padding-inline: var(--space-2);

  background-color: transparent;
  color: var(--text);
  border-color: transparent;
}

.btn--ghost:hover {
  color: var(--accent-ink);
  border-color: transparent;
}

/* --- On the ink ground --------------------------------------------------- */

.section--ink .btn--primary {
  background-color: var(--accent-on-ink);
  color: var(--ink);                 /* 6.11:1 — verified                    */
  border-color: var(--accent-on-ink);
}

.section--ink .btn--primary:hover {
  background-color: var(--text-on-ink);
  color: var(--ink);
  border-color: var(--text-on-ink);
}

.section--ink .btn--secondary {
  color: var(--text-on-ink);
  border-color: var(--text-muted-on-ink);
}

.section--ink .btn--secondary:hover {
  background-color: transparent;
  color: var(--text-on-ink);
  border-color: var(--text-on-ink);
}

/* --- Shared states ------------------------------------------------------- */

.btn:active { transform: translateY(1px); }

.btn[disabled],
.btn[aria-disabled="true"] {
  opacity: 0.55;
  cursor: not-allowed;
  pointer-events: none;
}

/* Loading: the label stays readable — never replaced by a spinner alone.
   The rule beneath it animates. */
.btn[aria-busy="true"] {
  position: relative;
  cursor: progress;
  pointer-events: none;
}

.btn[aria-busy="true"]::after {
  content: "";

  position: absolute;
  inset-block-end: 0;
  inset-inline-start: 0;

  width: 100%;
  height: var(--border-w-strong);

  background-color: currentColor;
  opacity: 0.6;
  transform-origin: left center;
  animation: btn-loading 1.1s var(--ease) infinite;
}

@keyframes btn-loading {
  0%   { transform: scaleX(0); }
  50%  { transform: scaleX(1); }
  100% { transform: scaleX(0); transform-origin: right center; }
}

@media (prefers-reduced-motion: reduce) {
  .btn:active { transform: none; }

  .btn[aria-busy="true"]::after {
    animation: none;
    opacity: 0.4;
  }
}

/* --- Size variants ------------------------------------------------------- */

.btn--lg {
  min-height: 3.25rem;
  padding-inline: var(--space-7);
  font-size: var(--fs-sm);
}

.btn--block {
  width: 100%;
  white-space: normal;
}

/* --- Text link that behaves like a call to action ------------------------ */

.link-cta {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);

  color: var(--accent);
  font-size: var(--fs-xs);
  font-weight: var(--fw-semibold);
  letter-spacing: var(--ls-button);
  text-decoration: none;

  border-block-end: var(--border-w-strong) solid var(--accent);
  padding-block-end: var(--space-1);
  transition:
    color var(--dur-fast) var(--ease),
    border-color var(--dur-fast) var(--ease),
    gap var(--dur-fast) var(--ease);
}

.link-cta:hover {
  color: var(--text);
  gap: var(--space-3);
  border-color: var(--text);
}

.link-cta__arrow {
  width: 0.9em;
  height: 0.9em;
  flex: none;
}

@media (prefers-reduced-motion: reduce) {
  .link-cta:hover { gap: var(--space-2); }
}