/* Subnet Trainer styles. Status is never conveyed by color alone (FR-011):
   correct/incorrect/locked also carry text + an icon/shape. Contrast targets
   WCAG AA. */

:root {
  --bg: #0f1626;
  --surface: #1b2740;
  --surface-2: #243352;
  --text: #f2f5fb; /* on --bg: contrast > 13:1 */
  --muted: #b9c4dc; /* on --bg: contrast > 7:1 */
  --accent: #6ea8fe;
  --correct: #4ade80;
  --incorrect: #f87171;
  --focus: #ffd166;
  --radius: 10px;
  --space: 1rem;
  font-family:
    system-ui,
    -apple-system,
    Segoe UI,
    Roboto,
    sans-serif;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  line-height: 1.5;
}

.visually-hidden {
  position: absolute;
  width: 1px;
  height: 1px;
  margin: -1px;
  padding: 0;
  overflow: hidden;
  clip: rect(0 0 0 0);
  white-space: nowrap;
  border: 0;
}

.skip-link {
  position: absolute;
  left: -999px;
  top: 0;
  background: var(--accent);
  color: #04132e;
  padding: 0.5rem 1rem;
  z-index: 10;
}
.skip-link:focus {
  left: 0;
}

.app-header {
  text-align: center;
  padding: var(--space);
}
.app-header h1 {
  margin: 0;
}
.tagline {
  color: var(--muted);
  margin: 0.25rem 0 0;
}

.app {
  max-width: 40rem;
  margin: 0 auto;
  padding: var(--space);
}

.card {
  background: var(--surface);
  border-radius: var(--radius);
  padding: 1.5rem;
  margin-bottom: var(--space);
}

/* Focus is always visible (keyboard operability, FR-012). */
:focus-visible {
  outline: 3px solid var(--focus);
  outline-offset: 2px;
}

button,
.option {
  font: inherit;
  cursor: pointer;
  border-radius: var(--radius);
  border: 2px solid var(--surface-2);
  background: var(--surface-2);
  color: var(--text);
  padding: 0.75rem 1rem;
}
button:hover,
.option:hover {
  border-color: var(--accent);
}

.btn-primary {
  background: var(--accent);
  color: #04132e;
  border-color: var(--accent);
  font-weight: 600;
}

.options {
  display: grid;
  gap: 0.5rem;
}

.answer-input {
  font: inherit;
  padding: 0.75rem;
  width: 100%;
  border-radius: var(--radius);
  border: 2px solid var(--surface-2);
  background: #0b1220;
  color: var(--text);
}

.prompt {
  font-size: 1.15rem;
}
.format-hint {
  color: var(--muted);
  font-size: 0.9rem;
}

/* Feedback: text + icon + color (never color alone). */
.feedback {
  border-left: 6px solid var(--surface-2);
  padding-left: 1rem;
}
.feedback--correct {
  border-left-color: var(--correct);
}
.feedback--incorrect {
  border-left-color: var(--incorrect);
}
.feedback__icon {
  font-weight: 700;
  margin-right: 0.4rem;
}

.derivation {
  background: #0b1220;
  border-radius: var(--radius);
  padding: 0.75rem 1rem;
}
.derivation ol {
  margin: 0;
  padding-left: 1.25rem;
}

/* Tier map. Locked tiers carry a lock glyph + "Locked" text, not color alone. */
.tier-list {
  list-style: none;
  padding: 0;
  display: grid;
  gap: 0.5rem;
}
.tier {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 0.75rem 1rem;
  background: var(--surface-2);
  border-radius: var(--radius);
}
.tier--locked {
  opacity: 0.75;
}
.tier__status {
  font-size: 0.9rem;
  color: var(--muted);
}

.stats {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(8rem, 1fr));
  gap: 0.5rem;
}
.stat {
  background: var(--surface-2);
  border-radius: var(--radius);
  padding: 0.75rem;
  text-align: center;
}
.stat__value {
  font-size: 1.5rem;
  font-weight: 700;
}
.stat__label {
  color: var(--muted);
  font-size: 0.85rem;
}

@media (prefers-reduced-motion: reduce) {
  * {
    transition: none !important;
    animation: none !important;
  }
}