/* Git Learning Lab — P1 skeleton styles.
   Deliberately minimal: no design system, no theming, no polish beyond the
   UX skill's practical baseline (semantic markup, visible focus, no
   color-only signaling, no broken narrow-width layout). Real visual design
   is P2+ work. */

:root {
  color-scheme: light;
  --color-bg: #ffffff;
  --color-text: #1a1a1a;
  --color-accent: #2b5fd9;
  --color-border: #d0d0d0;
  --space-1: 0.5rem;
  --space-2: 1rem;
  --space-3: 1.5rem;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: system-ui, -apple-system, "Segoe UI", sans-serif;
  color: var(--color-text);
  background: var(--color-bg);
  line-height: 1.5;
}

.app-header,
.app-nav,
.app-main,
.app-footer {
  padding: var(--space-2);
  max-width: 960px;
  margin: 0 auto;
}

.app-header h1 {
  margin: 0 0 var(--space-1) 0;
  font-size: 1.5rem;
}

.tagline {
  margin: 0;
  color: #555;
}

.app-nav {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-1);
  border-bottom: 1px solid var(--color-border);
}

.nav-btn {
  font: inherit;
  padding: var(--space-1) var(--space-2);
  border: 1px solid var(--color-border);
  border-radius: 6px 6px 0 0;
  background: #f5f5f5;
  color: var(--color-text);
  cursor: pointer;
}

.nav-btn[aria-current="true"] {
  background: var(--color-accent);
  color: #ffffff;
  border-color: var(--color-accent);
}

/* Never rely on color alone for the current-section signal (A11Y-003). */
.nav-btn[aria-current="true"]::after {
  content: " •";
}

.nav-btn:focus-visible,
button:focus-visible,
a:focus-visible {
  outline: 3px solid #ff8c00;
  outline-offset: 2px;
}

.panel {
  padding-top: var(--space-3);
}

.app-footer {
  margin-top: var(--space-3);
  border-top: 1px solid var(--color-border);
  color: #555;
  font-size: 0.9rem;
}

/* Narrow-viewport check (RESP-001): stack nav, keep touch targets reasonable. */
@media (max-width: 420px) {
  .app-nav {
    flex-direction: column;
  }

  .nav-btn {
    width: 100%;
    text-align: left;
    padding: var(--space-2);
  }
}