.top-nav,
.top-nav * {
  box-sizing: border-box;
}

.top-nav {
  position: sticky;
  top: 0;
  z-index: 1000;
  width: 100%;
  background: rgba(15, 17, 23, 0.92);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid #2e3248;
  padding: 0 1.5rem;
  font-family: 'Segoe UI', system-ui, sans-serif;
}

.top-nav-inner {
  max-width: 1100px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  gap: 0.25rem;
  height: 52px;
  overflow-x: auto;
  scrollbar-width: none;
}

.top-nav-inner::-webkit-scrollbar {
  display: none;
}

.nav-logo {
  font-size: 0.85rem;
  font-weight: 800;
  color: #7c6af7;
  letter-spacing: 0.04em;
  white-space: nowrap;
  margin-right: 1rem;
  flex-shrink: 0;
  text-decoration: none;
}

.nav-divider {
  width: 1px;
  height: 20px;
  background: #2e3248;
  margin-right: 1rem;
  flex-shrink: 0;
}

.nav-tab {
  display: flex;
  align-items: center;
  gap: 0.4rem;
  padding: 0.35rem 0.85rem;
  border-radius: 8px;
  text-decoration: none;
  font-size: 0.82rem;
  font-weight: 600;
  line-height: 1.2;
  white-space: nowrap;
  flex-shrink: 0;
  transition: background .15s, color .15s;
  color: #94a3b8;
}

.nav-tab:hover {
  background: #242736;
  color: #e2e8f0;
}

.nav-tab.active {
  background: rgba(124, 106, 247, .15);
  color: #7c6af7;
}

.nav-dot {
  width: 6px;
  height: 6px;
  border-radius: 50%;
  flex-shrink: 0;
}

body #back-home-btn,
body #back-btn {
  top: 5px;
  z-index: 1100;
  background: var(--surface);
  border-color: var(--accent);
  color: var(--accent);
}

body #back-home-btn:hover,
body #back-btn:hover {
  background: var(--surface2);
  border-color: var(--accent);
  color: var(--accent);
}

.lesson-nav {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 8px;
  max-width: 920px;
  margin: 0 auto 22px;
}

.lesson-link {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 30px;
  padding: 5px 11px;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: var(--surface);
  color: var(--text-dim);
  font-size: 12px;
  font-weight: 700;
  line-height: 1.2;
  text-decoration: none;
  white-space: nowrap;
  transition: background .15s, border-color .15s, color .15s, transform .15s;
}

.lesson-link:hover,
.lesson-link.active {
  background: var(--surface2);
  border-color: var(--accent);
  color: var(--accent);
}

.lesson-link:hover {
  transform: translateY(-1px);
}

@media (max-width: 600px) {
  .top-nav {
    padding: 0 1rem;
  }

  .lesson-nav {
    justify-content: flex-start;
    overflow-x: auto;
    flex-wrap: nowrap;
    scrollbar-width: none;
  }

  .lesson-nav::-webkit-scrollbar {
    display: none;
  }
}

@media (max-width: 1220px) {
  body:has(#back-home-btn) .top-nav,
  body:has(#back-btn) .top-nav {
    padding-left: 72px;
  }
}