/* ==========================================================================
   Sidebar Navigation Styles
   ========================================================================== */

.sidebar {
  width: var(--sidebar-width);
  height: 100vh;
  background: var(--bg-surface);
  border-right: 1px solid var(--border-color);
  display: flex;
  flex-direction: column;
  transition: width var(--transition-smooth), transform var(--transition-smooth);
  z-index: 100;
  flex-shrink: 0;
  position: relative;
}

/* App Branding / Logo Area */
.sidebar-header {
  padding: 1.5rem 1.25rem 1.25rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  border-bottom: 1px solid var(--border-subtle);
}

.brand {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  overflow: hidden;
}

.brand-icon {
  width: 40px;
  height: 40px;
  border-radius: var(--radius-md);
  background: linear-gradient(135deg, #4f46e5, #06b6d4);
  display: flex;
  align-items: center;
  justify-content: center;
  color: #fff;
  font-weight: 800;
  font-size: 1.2rem;
  box-shadow: 0 4px 12px rgba(79, 70, 229, 0.3);
  flex-shrink: 0;
}

.brand-info {
  display: flex;
  flex-direction: column;
  transition: opacity var(--transition-fast);
}

.brand-title {
  font-size: 1.05rem;
  font-weight: 700;
  letter-spacing: -0.02em;
  color: var(--text-primary);
  line-height: 1.2;
}

.brand-subtitle {
  font-size: 0.72rem;
  color: var(--primary);
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.sidebar-toggle-btn {
  color: var(--text-muted);
  width: 32px;
  height: 32px;
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  transition: background var(--transition-fast), color var(--transition-fast);
}

.sidebar-toggle-btn:hover {
  background: var(--bg-surface-elevated);
  color: var(--text-primary);
}

/* Nav Menu Items */
.sidebar-nav {
  flex: 1;
  overflow-y: auto;
  padding: 1rem 0.85rem;
  display: flex;
  flex-direction: column;
  gap: 1.25rem;
}

.nav-group {
  display: flex;
  flex-direction: column;
  gap: 0.25rem;
}

.nav-group-label {
  font-size: 0.68rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-muted);
  padding: 0.4rem 0.75rem;
}

.nav-item {
  display: flex;
  align-items: center;
  gap: 0.85rem;
  padding: 0.7rem 0.85rem;
  border-radius: var(--radius-md);
  color: var(--text-secondary);
  font-weight: 500;
  font-size: 0.88rem;
  transition: all var(--transition-fast);
  position: relative;
  user-select: none;
}

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

.nav-item.active {
  background: var(--primary-light);
  color: var(--primary);
  font-weight: 600;
}

.nav-item.active::before {
  content: '';
  position: absolute;
  left: 0;
  top: 15%;
  height: 70%;
  width: 4px;
  background: var(--primary);
  border-radius: 0 4px 4px 0;
}

.nav-icon {
  width: 20px;
  height: 20px;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
}

.nav-label {
  flex: 1;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.nav-badge {
  font-size: 0.72rem;
  font-weight: 600;
  padding: 0.15rem 0.5rem;
  border-radius: var(--radius-full);
  background: var(--bg-surface-elevated);
  color: var(--text-secondary);
}

.nav-item.active .nav-badge {
  background: var(--primary);
  color: #fff;
}

.nav-badge.danger {
  background: var(--danger-bg);
  color: var(--danger);
}

/* Sidebar Footer */
.sidebar-footer {
  padding: 1rem 1.25rem;
  border-top: 1px solid var(--border-subtle);
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.user-study-card {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  width: 100%;
  background: var(--bg-surface-elevated);
  padding: 0.65rem 0.75rem;
  border-radius: var(--radius-md);
  border: 1px solid var(--border-color);
}

.study-progress-circle {
  width: 34px;
  height: 34px;
  position: relative;
  display: flex;
  align-items: center;
  justify-content: center;
}

.study-info {
  flex: 1;
  display: flex;
  flex-direction: column;
}

.study-info-title {
  font-size: 0.78rem;
  font-weight: 600;
  color: var(--text-primary);
}

.study-info-sub {
  font-size: 0.7rem;
  color: var(--text-muted);
}

/* ==========================================================================
   Mobile Sidebar Drawer Styles
   ========================================================================== */

.sidebar-backdrop {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.5);
  backdrop-filter: blur(4px);
  z-index: 999;
  opacity: 0;
  pointer-events: none;
  transition: opacity var(--transition-normal);
}

.sidebar-backdrop.active {
  opacity: 1;
  pointer-events: auto;
}

@media (max-width: 900px) {
  .sidebar {
    position: fixed;
    top: 0;
    left: 0;
    bottom: 0;
    width: 290px;
    transform: translateX(-100%);
    box-shadow: var(--shadow-lg);
    z-index: 1000;
  }

  .sidebar.open {
    transform: translateX(0);
  }
}