/* ── LAYOUT ── */
.shell { display: flex; height: 100vh; }

/* ── SIDEBAR ── */
.sidebar {
  width: 256px;
  background: var(--surface);
  border-right: 1px solid var(--border);
  color: var(--text);
  display: flex;
  flex-direction: column;
  flex-shrink: 0;
  position: sticky;
  top: 0;
  height: 100vh;
  overflow-y: auto;
  overflow-x: hidden;
  transition: transform .25s;
  /* Subtle left indicator strip */
  box-shadow: inset -1px 0 0 var(--border);
}

.sb-logo {
  padding: 20px 18px 14px;
  border-bottom: 1px solid var(--border);
}
.sb-brand {
  font-family: 'Rajdhani', sans-serif;
  font-size: 18px;
  font-weight: 700;
  letter-spacing: .08em;
  text-transform: uppercase;
  color: var(--navy);
  text-shadow: var(--glow-cyan);
}
.sb-sub {
  font-family: 'JetBrains Mono', monospace;
  font-size: 9px;
  color: var(--hint);
  margin-top: 2px;
  text-transform: uppercase;
  letter-spacing: 1px;
}

/* Streak / XP bar */
.sb-streak {
  padding: 8px 16px;
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 11px;
  color: var(--muted);
  border-bottom: 1px solid var(--border);
}
.sb-streak .streak-fire { font-size: 15px; }
.sb-streak .streak-num {
  font-family: 'JetBrains Mono', monospace;
  font-weight: 600;
  color: var(--amber);
  font-size: 14px;
}
.sb-xp-bar {
  height: 2px;
  background: var(--border);
  border-radius: 1px;
  flex: 1;
  margin-top: 2px;
}
.sb-xp-fill {
  height: 2px;
  background: linear-gradient(90deg, var(--amber), var(--gold));
  border-radius: 1px;
  transition: width .6s cubic-bezier(.4,0,.2,1);
  box-shadow: var(--glow-amber);
}
.sb-xp-label {
  font-family: 'JetBrains Mono', monospace;
  font-size: 9px;
  color: var(--hint);
  margin-top: 2px;
}

/* Sidebar sections */
.sb-section {
  padding: 14px 16px 4px;
  font-family: 'JetBrains Mono', monospace;
  font-size: 9px;
  text-transform: uppercase;
  letter-spacing: 1.4px;
  color: var(--hint);
}
.sb-item {
  display: flex;
  align-items: center;
  gap: 9px;
  padding: 8px 14px 8px 16px;
  margin: 1px 8px;
  border-radius: var(--r);
  cursor: pointer;
  font-size: 13px;
  color: var(--muted);
  border: none;
  background: none;
  width: calc(100% - 16px);
  text-align: left;
  transition: all .15s;
  position: relative;
}
.sb-item::before {
  content: '';
  position: absolute;
  left: 0;
  top: 50%;
  transform: translateY(-50%);
  width: 2px;
  height: 0;
  background: var(--navy);
  border-radius: 0 2px 2px 0;
  transition: height .15s;
}
.sb-item:hover {
  background: rgba(56,189,248,.06);
  color: var(--text);
}
.sb-item.on {
  background: rgba(56,189,248,.1);
  color: var(--navy);
  font-weight: 500;
}
.sb-item.on::before { height: 70%; }
.sb-item.done-nav .sb-dot { background: var(--green); }
.sb-dot {
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: var(--border2);
  flex-shrink: 0;
  transition: background .2s;
}
.sb-item.on .sb-dot { background: var(--navy); box-shadow: var(--glow-cyan); }
.sb-badge {
  margin-left: auto;
  font-family: 'JetBrains Mono', monospace;
  font-size: 10px;
  padding: 1px 6px;
  border-radius: 20px;
  background: var(--border2);
  color: var(--muted);
}
.sb-footer {
  margin-top: auto;
  padding: 12px 16px;
  border-top: 1px solid var(--border);
}
.sb-prog-label {
  font-family: 'JetBrains Mono', monospace;
  font-size: 10px;
  color: var(--hint);
  margin-bottom: 5px;
}
.sb-prog {
  height: 2px;
  background: var(--border);
  border-radius: 1px;
}
.sb-prog-fill {
  height: 2px;
  background: var(--green);
  border-radius: 1px;
  transition: width .4s;
  box-shadow: var(--glow-green);
}

/* ── MAIN ── */
.main {
  flex: 1;
  overflow-y: auto;
  /* Subtle dot-grid overlay */
  background-image:
    radial-gradient(circle, var(--grid-color) 1px, transparent 1px);
  background-size: 28px 28px;
  background-attachment: fixed;
}
.view {
  display: none;
  padding: 40px 52px;
  max-width: 960px;
}
.view.on { display: block; }

/* ── TOPBAR ── */
.topbar {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 28px;
}
.btn-back {
  display: flex;
  align-items: center;
  gap: 6px;
  padding: 6px 13px;
  border: 1px solid var(--border);
  border-radius: var(--r);
  background: var(--surface);
  cursor: pointer;
  font-size: 12px;
  color: var(--muted);
  transition: all .15s;
}
.btn-back:hover {
  border-color: var(--navy);
  color: var(--navy);
  box-shadow: var(--glow-cyan);
}
.topbar-title {
  font-family: 'JetBrains Mono', monospace;
  font-size: 11px;
  color: var(--hint);
  letter-spacing: .5px;
}

/* ── MOBILE ── */
.mob-menu {
  display: none;
  position: fixed;
  top: 12px;
  left: 12px;
  z-index: 200;
  width: 36px;
  height: 36px;
  background: var(--surface);
  color: var(--navy);
  border: 1px solid var(--border);
  border-radius: var(--r);
  cursor: pointer;
  font-size: 16px;
  align-items: center;
  justify-content: center;
}
@media(max-width:768px) {
  .mob-menu { display: flex; }
  .sidebar { position: fixed; z-index: 100; transform: translateX(-100%); height: 100vh; }
  .sidebar.open { transform: translateX(0); }
  .view { padding: 60px 18px 24px; }
  .stats-row { grid-template-columns: repeat(2,1fr); }
  .topic-grid, .how-grid, .prog-grid, .ss-grid { grid-template-columns: 1fr; }
  .step-tabs { flex-wrap: wrap; }
}