:root {
  --bg: #050b14;
  --bg-card: #0c1524;
  --cyan: #00e5ff;
  --green: #39ff14;
  --text: #d7e2f0;
  --muted: #7f92ab;
  --danger: #ff4d6d;
  --warn: #ffb703;
  --border: #1a2a44;
}

* { box-sizing: border-box; }
body {
  margin: 0;
  font-family: "Segoe UI", system-ui, sans-serif;
  background: var(--bg);
  color: var(--text);
  min-height: 100vh;
}
.grid-bg {
  background-image:
    linear-gradient(rgba(0, 229, 255, 0.04) 1px, transparent 1px),
    linear-gradient(90deg, rgba(0, 229, 255, 0.04) 1px, transparent 1px);
  background-size: 32px 32px;
}
.disclaimer-banner {
  background: #2a1020;
  color: #ffc9d6;
  text-align: center;
  padding: 0.5rem 1rem;
  font-size: 0.85rem;
  border-bottom: 1px solid #5c2030;
}
.site-header {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 1rem;
  padding: 1rem 1.5rem;
  border-bottom: 1px solid var(--border);
  background: rgba(5, 11, 20, 0.92);
  position: sticky;
  top: 0;
  z-index: 10;
}
.logo {
  font-weight: 700;
  color: var(--text);
  text-decoration: none;
  letter-spacing: 0.04em;
}
.logo span { color: var(--cyan); }
nav a {
  color: var(--muted);
  text-decoration: none;
  margin-right: 1rem;
}
nav a:hover, nav a:focus-visible { color: var(--cyan); outline: none; }
.user-menu { margin-left: auto; display: flex; align-items: center; gap: 0.75rem; }
.user-pill {
  border: 1px solid var(--border);
  padding: 0.25rem 0.75rem;
  border-radius: 999px;
  font-size: 0.85rem;
}
.container { max-width: 1100px; margin: 0 auto; padding: 1.5rem; }
.hero { padding: 2rem 0 3rem; }
.hero h1 { font-size: clamp(2rem, 5vw, 3rem); margin-bottom: 0.5rem; }
.hero .accent { color: var(--green); }
.eyebrow { color: var(--cyan); text-transform: uppercase; letter-spacing: 0.12em; font-size: 0.75rem; }
.lead { color: var(--muted); max-width: 60ch; }
.card-grid {
  display: grid;
  gap: 1rem;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
}
.card-grid.three { grid-template-columns: repeat(auto-fit, minmax(280px, 1fr)); }
.card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 1.25rem;
  box-shadow: 0 0 0 1px rgba(0, 229, 255, 0.03);
}
.card-link { text-decoration: none; color: inherit; transition: border-color 0.2s, transform 0.2s; }
.card-link:hover, .card-link:focus-visible {
  border-color: var(--cyan);
  transform: translateY(-2px);
  outline: 2px solid var(--cyan);
  outline-offset: 2px;
}
.card-cta { color: var(--green); font-size: 0.9rem; }
.dashboard-cards h2 { color: var(--cyan); font-size: 1.1rem; }
.btn {
  display: inline-block;
  padding: 0.55rem 1rem;
  border-radius: 8px;
  border: 1px solid transparent;
  cursor: pointer;
  text-decoration: none;
  font-weight: 600;
}
.btn-primary {
  background: linear-gradient(135deg, #007a8a, var(--cyan));
  color: #001018;
}
.btn-ghost {
  background: transparent;
  border-color: var(--border);
  color: var(--text);
}
.btn:focus-visible { outline: 2px solid var(--green); outline-offset: 2px; }
.stack-form label { display: block; margin-bottom: 0.75rem; }
.stack-form input, .stack-form textarea, .stack-form select {
  width: 100%;
  margin-top: 0.35rem;
  padding: 0.6rem;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: #060e1a;
  color: var(--text);
}
.stack-form input:focus-visible, .stack-form textarea:focus-visible {
  outline: 2px solid var(--cyan);
  border-color: var(--cyan);
}
.inline-form { display: inline; }
.breadcrumbs { color: var(--muted); margin-bottom: 1rem; font-size: 0.9rem; }
.breadcrumbs a { color: var(--cyan); }
.toast-container { position: fixed; top: 4.5rem; right: 1rem; z-index: 20; }
.toast {
  padding: 0.75rem 1rem;
  margin-bottom: 0.5rem;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: var(--bg-card);
}
.toast-success { border-color: var(--green); }
.toast-error { border-color: var(--danger); }
.toast-warning { border-color: var(--warn); }
.tag {
  display: inline-block;
  font-size: 0.75rem;
  padding: 0.15rem 0.5rem;
  border-radius: 4px;
  background: #12243a;
  color: var(--cyan);
  margin-bottom: 0.5rem;
}
.tag-easy { color: var(--green); }
.tag-medium { color: var(--warn); }
.tag-hard { color: var(--danger); }
.code, pre.result-box {
  font-family: Consolas, "Courier New", monospace;
  background: #02060d;
  border: 1px solid var(--border);
  padding: 1rem;
  border-radius: 8px;
  overflow-x: auto;
  font-size: 0.85rem;
}
.warn { color: var(--warn); font-size: 0.85rem; }
.muted { color: var(--muted); }
.success { color: var(--green); }
.error { color: var(--danger); }
.lab-panel { border-color: #3a2030; }
table { width: 100%; border-collapse: collapse; }
th, td { padding: 0.65rem; text-align: left; border-bottom: 1px solid var(--border); }
tr.highlight { background: rgba(0, 229, 255, 0.08); }
.badge-done { color: var(--green); font-size: 0.8rem; }
.card.done { opacity: 0.85; border-color: var(--green); }
.site-footer {
  text-align: center;
  color: var(--muted);
  padding: 2rem;
  border-top: 1px solid var(--border);
  margin-top: 2rem;
}
.lesson-body pre.code {
  display: block;
  white-space: pre-wrap;
}
.radio-row { display: flex; gap: 0.5rem; align-items: center; }
.hero-actions { display: flex; gap: 0.75rem; flex-wrap: wrap; margin-top: 1.5rem; }
.auth-card { max-width: 420px; }
.table-wrap { overflow-x: auto; }
@media (max-width: 640px) {
  .site-header { flex-direction: column; align-items: flex-start; }
  .user-menu { margin-left: 0; }
}