:root {
  --bg-top: #f5fbff;
  --bg-bottom: #d7e7ff;
  --panel: rgba(255, 255, 255, 0.86);
  --panel-border: rgba(21, 48, 77, 0.12);
  --ink: #15304d;
  --muted: #5b738c;
  --accent: #0f766e;
  --accent-strong: #0d9488;
  --shadow: 0 24px 60px rgba(19, 48, 77, 0.14);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  font-family: "Trebuchet MS", "Gill Sans", "Segoe UI", sans-serif;
  color: var(--ink);
  background:
    radial-gradient(circle at top left, rgba(255,255,255,0.92), transparent 28%),
    linear-gradient(180deg, var(--bg-top), var(--bg-bottom));
}

.page {
  width: min(1380px, calc(100% - 2rem));
  margin: 0 auto;
  padding: 1.5rem 0 2rem;
}

.panel {
  background: var(--panel);
  border: 1px solid var(--panel-border);
  border-radius: 24px;
  box-shadow: var(--shadow);
  backdrop-filter: blur(14px);
}

.hero {
  padding: 1.4rem 1.5rem;
  margin-bottom: 1rem;
}

.eyebrow,
.topic-label {
  margin: 0 0 0.35rem;
  color: var(--accent);
  font-size: 0.9rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

h1,
h2,
h3 {
  margin: 0;
}

h1 {
  font-size: clamp(2rem, 5vw, 3.7rem);
  line-height: 0.95;
}

.intro {
  max-width: 78ch;
  margin: 0.75rem 0 0;
  color: var(--muted);
  font-size: 1rem;
}

.topic-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 1rem;
}

.topic-card {
  padding: 1.2rem;
}

.topic-header {
  margin-bottom: 1rem;
}

.topic-header h2 {
  font-size: 1.7rem;
}

.subtopic-block {
  padding: 0.95rem 0;
  border-top: 1px solid rgba(21, 48, 77, 0.1);
}

.subtopic-block:first-of-type {
  border-top: 0;
  padding-top: 0;
}

.subtopic-block h3 {
  font-size: 1.06rem;
  margin-bottom: 0.35rem;
}

.concepts {
  margin: 0;
  color: var(--muted);
  line-height: 1.45;
}

.status {
  display: inline-block;
  margin: 0.7rem 0 0;
  padding: 0.34rem 0.62rem;
  border-radius: 999px;
  font-size: 0.86rem;
  font-weight: 700;
  color: var(--accent);
  background: rgba(15, 118, 110, 0.1);
}

.current-block {
  background: rgba(219, 239, 255, 0.45);
  border-radius: 18px;
  padding: 1rem;
  border-top: 0;
}

.link-list {
  display: grid;
  gap: 0.55rem;
  margin-top: 0.8rem;
}

.app-link {
  display: block;
  padding: 0.8rem 0.9rem;
  border-radius: 16px;
  text-decoration: none;
  font-weight: 700;
  color: var(--ink);
  background: rgba(255,255,255,0.92);
  border: 1px solid rgba(21,48,77,0.12);
}

.app-link:hover {
  background: white;
  transform: translateY(-1px);
}

@media (max-width: 1100px) {
  .topic-grid {
    grid-template-columns: 1fr;
  }
}