:root {
  color-scheme: light dark;
  --bg: #ffffff;
  --fg: #1a1a1a;
  --muted: #666666;
  --border: #dddddd;
  --accent: #2f6f4f;
  --danger: #b3261e;
  --code-bg: #f5f5f5;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #16181c;
    --fg: #e8e8e8;
    --muted: #9a9a9a;
    --border: #333740;
    --accent: #5fb98a;
    --danger: #ff6b60;
    --code-bg: #20232a;
  }
}

* { box-sizing: border-box; }

body {
  margin: 0;
  font-family: -apple-system, Segoe UI, Roboto, Helvetica, Arial, sans-serif;
  background: var(--bg);
  color: var(--fg);
  line-height: 1.5;
}

.site-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 1rem 1.5rem;
  border-bottom: 1px solid var(--border);
}

.site-header .brand {
  font-weight: 700;
  font-size: 1.1rem;
  text-decoration: none;
  color: var(--fg);
}

.site-header nav a {
  margin-left: 1rem;
  color: var(--muted);
  text-decoration: none;
}

.site-header nav a:hover { color: var(--fg); }

.header-right {
  display: flex;
  align-items: center;
  gap: 1rem;
}

.stats-badge {
  font-size: 0.9rem;
  color: var(--muted);
  white-space: nowrap;
}

main {
  max-width: 780px;
  margin: 0 auto;
  padding: 1.5rem;
}

.flashes {
  list-style: none;
  margin: 1rem auto 0;
  max-width: 780px;
  padding: 0.75rem 1rem;
  background: var(--danger);
  color: #fff;
  border-radius: 6px;
}

.login-form {
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
  max-width: 320px;
}

.login-form input {
  padding: 0.5rem;
  border: 1px solid var(--border);
  border-radius: 6px;
  background: var(--bg);
  color: var(--fg);
}

button {
  cursor: pointer;
  padding: 0.5rem 1rem;
  border-radius: 6px;
  border: 1px solid var(--accent);
  background: var(--accent);
  color: #fff;
  font-size: 1rem;
}

button:disabled { opacity: 0.6; cursor: default; }

.lesson-list { list-style: none; padding: 0; }

.lesson-list li { border: 1px solid var(--border); border-radius: 8px; margin-bottom: 0.75rem; }

.lesson-list a {
  display: flex;
  justify-content: space-between;
  padding: 1rem;
  text-decoration: none;
  color: var(--fg);
}

.lesson-progress { color: var(--muted); }

.theory pre, .run-output {
  background: var(--code-bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 1rem;
  white-space: pre-wrap;
  font-family: SFMono-Regular, Consolas, "Liberation Mono", monospace;
}

.exercise {
  border-top: 1px solid var(--border);
  padding-top: 1.5rem;
  margin-top: 1.5rem;
}

.badge-done {
  color: var(--accent);
  font-size: 0.9rem;
  font-weight: normal;
  margin-left: 0.5rem;
}

.quiz {
  background: var(--code-bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 1rem;
  margin: 0.75rem 0;
}

.quiz-question {
  margin-top: 0;
  font-weight: 600;
}

.quiz-options {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.quiz-option {
  background: var(--bg);
  color: var(--fg);
  border: 1px solid var(--border);
  text-align: left;
}

.quiz-option:hover { border-color: var(--accent); }

.quiz-feedback {
  color: var(--danger);
  min-height: 1.2em;
  margin-bottom: 0;
}

.quiz-feedback:empty { margin: 0; }

.code-editor {
  width: 100%;
  font-family: SFMono-Regular, Consolas, "Liberation Mono", monospace;
  font-size: 0.95rem;
  background: var(--code-bg);
  color: var(--fg);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 0.75rem;
  tab-size: 4;
}

.exercise-actions {
  display: flex;
  align-items: center;
  gap: 1rem;
  margin: 0.75rem 0;
}

.run-status.passed { color: var(--accent); }
.run-status.failed { color: var(--danger); }

.run-output:empty { display: none; }

.progress-bar {
  background: var(--code-bg);
  border: 1px solid var(--border);
  border-radius: 999px;
  height: 10px;
  overflow: hidden;
  margin: 0.75rem 0 1.5rem;
}

.progress-bar-fill {
  background: var(--accent);
  height: 100%;
}

.progress-table { width: 100%; border-collapse: collapse; }

.progress-table th, .progress-table td {
  text-align: left;
  padding: 0.5rem;
  border-bottom: 1px solid var(--border);
}