*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

:root {
  --green: #3ce78c;
  --green-dim: rgba(60, 231, 140, 0.10);
  --green-border: rgba(60, 231, 140, 0.22);
  --bg: #0d0d0d;
  --surface: #121212;
  --surface-2: #181818;
  --border: #1f1f1f;
  --border-2: #2a2a2a;
  --text: #f0f0f0;
  --text-muted: #777;
  --sidebar-w: 240px;
  --radius: 12px;
}

html, body {
  height: 100%;
  font-family: 'Inter', system-ui, sans-serif;
  background: var(--bg);
  color: var(--text);
  -webkit-font-smoothing: antialiased;
}

/* Layout */
.layout {
  display: flex;
  height: 100vh;
  overflow: hidden;
}

/* Sidebar */
.sidebar {
  width: var(--sidebar-w);
  min-width: var(--sidebar-w);
  background: var(--surface);
  border-right: 1px solid var(--border);
  display: flex;
  flex-direction: column;
  padding: 24px 16px;
  overflow-y: auto;
}

.sidebar-logo {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 32px;
  padding: 0 4px;
}

.logo-icon {
  width: 28px;
  height: 28px;
  background: var(--green);
  color: #000;
  font-weight: 700;
  font-size: 13px;
  border-radius: 7px;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
}

.logo-text {
  font-size: 15px;
  font-weight: 700;
  letter-spacing: -0.2px;
}

.sidebar-label {
  font-size: 11px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.8px;
  color: var(--text-muted);
  padding: 0 8px;
  margin-bottom: 8px;
}

.sidebar-nav {
  display: flex;
  flex-direction: column;
  gap: 2px;
}

.nav-item {
  display: flex;
  align-items: flex-start;
  gap: 9px;
  width: 100%;
  background: none;
  border: none;
  color: var(--text-muted);
  font-size: 13.5px;
  font-family: inherit;
  text-align: left;
  padding: 9px 10px;
  border-radius: 8px;
  cursor: pointer;
  line-height: 1.4;
  transition: background 0.15s, color 0.15s;
}

.nav-item:hover {
  background: var(--surface-2);
  color: var(--text);
}

.nav-item.active {
  background: var(--green-dim);
  color: var(--green);
  border: 1px solid var(--green-border);
}

.nav-icon {
  margin-top: 1px;
  flex-shrink: 0;
  opacity: 0.6;
}

.nav-item.active .nav-icon {
  opacity: 1;
}

.nav-item--soon {
  cursor: default;
  opacity: 0.45;
}

.nav-item--soon:hover {
  background: none;
  color: var(--text-muted);
}

.nav-soon-text {
  display: flex;
  flex-direction: column;
  gap: 4px;
}

.soon-badge {
  font-size: 10px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.5px;
  color: var(--text-muted);
}

/* Content area */
.content {
  flex: 1;
  overflow-y: auto;
  padding: 48px 56px;
}

/* Welcome state */
.welcome-state {
  max-width: 580px;
  padding-top: 8px;
}

.welcome-tag {
  display: inline-block;
  font-size: 11px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.7px;
  color: var(--green);
  background: var(--green-dim);
  border: 1px solid var(--green-border);
  padding: 3px 10px;
  border-radius: 20px;
  margin-bottom: 20px;
}

.welcome-title {
  font-size: clamp(24px, 3vw, 32px);
  font-weight: 700;
  letter-spacing: -0.5px;
  line-height: 1.2;
  margin-bottom: 16px;
}

.welcome-desc {
  font-size: 15px;
  color: var(--text-muted);
  line-height: 1.7;
  margin-bottom: 12px;
}

.welcome-steps {
  margin-top: 32px;
  display: flex;
  flex-direction: column;
  gap: 12px;
  padding: 24px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
}

.welcome-step {
  display: flex;
  align-items: center;
  gap: 12px;
  font-size: 14px;
  color: var(--text-muted);
}

.step-dot {
  width: 7px;
  height: 7px;
  border-radius: 50%;
  background: var(--green);
  flex-shrink: 0;
}

/* Topic panel */
.topic-panel {
  max-width: 760px;
}

.topic-header {
  margin-bottom: 28px;
}

.topic-tag {
  display: inline-block;
  font-size: 11px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.7px;
  color: var(--green);
  background: var(--green-dim);
  border: 1px solid var(--green-border);
  padding: 3px 10px;
  border-radius: 20px;
  margin-bottom: 14px;
}

.topic-title {
  font-size: clamp(22px, 3vw, 30px);
  font-weight: 700;
  letter-spacing: -0.5px;
  line-height: 1.2;
  margin-bottom: 12px;
}

.topic-desc {
  font-size: 15px;
  color: var(--text-muted);
  line-height: 1.65;
  max-width: 600px;
}

/* Video */
.video-wrapper {
  width: 100%;
  border-radius: var(--radius);
  overflow: hidden;
  background: var(--surface-2);
  border: 1px solid var(--border-2);
  margin-bottom: 20px;
}

.video-wrapper iframe,
.video-wrapper video {
  display: block;
  width: 100%;
  aspect-ratio: 16 / 9;
  border: none;
  background: #000;
}

.video-placeholder {
  aspect-ratio: 16 / 9;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 12px;
  color: var(--text-muted);
  font-size: 13px;
}

/* Link */
.topic-link {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  background: var(--green);
  color: #000;
  font-size: 14px;
  font-weight: 600;
  font-family: inherit;
  padding: 11px 22px;
  border-radius: 9px;
  text-decoration: none;
  transition: opacity 0.15s;
}

.topic-link:hover {
  opacity: 0.85;
}

.topic-link-icon {
  display: flex;
  align-items: center;
}

/* Scrollbar */
::-webkit-scrollbar { width: 6px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--border-2); border-radius: 99px; }

/* Mobile */
@media (max-width: 640px) {
  .layout { flex-direction: column; height: auto; overflow: auto; }
  .sidebar { width: 100%; border-right: none; border-bottom: 1px solid var(--border); padding: 16px; }
  .sidebar-logo { margin-bottom: 16px; }
  .sidebar-nav { flex-direction: row; flex-wrap: wrap; gap: 6px; }
  .nav-item { width: auto; font-size: 13px; padding: 7px 10px; }
  .content { padding: 24px 20px; overflow-y: visible; }
}