/* ============================================================
   CCD BRB Design System — Buttons (Phase 1.16)
   ------------------------------------------------------------
   Single button vocabulary for every CCD·BRB tool.
   Imported on top of tokens.css. Opt-in.

   Namespace: .btn (base) + .btn-{variant}.
   Reserves .is-* for state (.is-loading, .is-selected).

   Spec: DESIGN-SYSTEM.md §19.
   ============================================================ */

/* ── Base ──────────────────────────────────────────────── */
.btn {
  --_h: 36px;                       /* default md size — matches .f-control row */
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--s-2);
  height: var(--_h);
  padding: 0 var(--s-4);
  font-family: inherit;
  font-size: var(--fs-small);
  font-weight: var(--fw-semi);
  line-height: 1;
  border: 1px solid transparent;
  border-radius: var(--r-pill);
  background: transparent;
  color: var(--ink);
  cursor: pointer;
  user-select: none;
  transition: background var(--dur-fast) var(--ease),
              border-color var(--dur-fast) var(--ease),
              box-shadow var(--dur-fast) var(--ease),
              transform var(--dur-fast) var(--ease),
              color var(--dur-fast) var(--ease);
}

.btn:focus-visible {
  outline: var(--focus-ring-width) solid var(--focus-ring-color);
  outline-offset: var(--focus-ring-offset);
}

.btn:active:not(:disabled):not(.is-loading):not(.btn-link) {
  transform: scale(0.98);
}

.btn:disabled,
.btn[aria-disabled="true"] {
  border-style: dashed;
  border-color: var(--rule);
  background: transparent;
  color: var(--ink-muted);
  opacity: 0.6;
  pointer-events: none;
}

/* ── Sizes ─────────────────────────────────────────────── */
.btn-sm { --_h: 28px; padding: 0 var(--s-3); font-size: var(--fs-micro); }
.btn-lg { --_h: 44px; padding: 0 var(--s-5); font-size: var(--fs-body); }

/* ── Variants ──────────────────────────────────────────── */

/* Primary — single most important action. One per surface. */
.btn-primary { background: var(--brand); color: var(--paper); }
.btn-primary:hover:not(:disabled) { box-shadow: var(--shadow-glow-brand); }

/* Strong — alternative primary, ink fill. Hero CTA, dramatic-on-paper. */
.btn-strong { background: var(--ink); color: var(--paper); }
.btn-strong:hover:not(:disabled) { background: var(--ink-soft); }

/* Ghost — paper + rule border. Secondary action paired with primary. */
.btn-ghost {
  background: var(--paper);
  color: var(--ink);
  border-color: var(--rule);
}
.btn-ghost:hover:not(:disabled) {
  background: var(--paper-tint);
  border-color: var(--ink-muted);
}

/* Soft — tint-neutral filled, no border. Tertiary in dense contexts.
   Sibling of the neutral pill: holds shape on tinted canvas because
   tint-neutral is categorical, not surface. */
.btn-soft { background: var(--tint-neutral); color: var(--ink); }
.btn-soft:hover:not(:disabled) { background: var(--heat-2); }

/* Link — text-only, brand. Inline action inside prose or compact cells. */
.btn-link {
  background: transparent;
  color: var(--brand);
  height: auto;
  padding: 0;
  border: 0;
  font-weight: var(--fw-medium);
  text-decoration: underline;
  text-underline-offset: 3px;
  text-decoration-thickness: 1px;
}
.btn-link:hover:not(:disabled) { text-decoration-thickness: 2px; }

/* Danger — rust fill. Destructive confirmation only. */
.btn-danger { background: var(--dot-negative); color: var(--paper); }
.btn-danger:hover:not(:disabled) { background: #9A4239; }

/* ── Modifiers ─────────────────────────────────────────── */

/* Icon-only — square, width = height. Requires aria-label. */
.btn-icon { padding: 0; width: var(--_h); }

/* Loading — dim label, kill pointer-events; pair with .icon.spin glyph. */
.btn.is-loading { pointer-events: none; }
.btn.is-loading .btn-label { opacity: 0.5; transition: opacity var(--dur-fast) var(--ease); }

/* ── Group (segmented row) ─────────────────────────────── */
.btn-group { display: inline-flex; gap: var(--s-2); }
.btn-group .btn.is-selected { background: var(--state-selected); }