/* ============================================================
   Layout System — Sidebar + Main Content + Drag Handle
   ============================================================ */

/* === Root Layout === */
.app {
  display: flex;
  flex-direction: column;
  min-height: 100vh;
}

/* === Header === */
.header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: var(--header-height);
  z-index: 100;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 24px;
  border-bottom: 1px solid var(--border-divider);
  background: rgba(247, 245, 242, 0.75);
  backdrop-filter: blur(20px) saturate(1.8);
  -webkit-backdrop-filter: blur(20px) saturate(1.8);
  transition: background var(--transition-base), border-color var(--transition-base);
}
[data-theme="dark"] .header {
  background: rgba(18, 18, 18, 0.75);
}

.header-left {
  display: flex;
  align-items: center;
  gap: 12px;
}

.header-logo {
  display: flex;
  align-items: center;
  gap: 10px;
  font-weight: 600;
  font-size: 1rem;
  color: var(--text-primary);
  letter-spacing: -0.01em;
}

.header-logo-icon {
  width: 28px;
  height: 28px;
  background: var(--brand-primary);
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  color: white;
  font-size: 14px;
  font-weight: 700;
  flex-shrink: 0;
}

.header-nav {
  display: flex;
  align-items: center;
  gap: 4px;
}

.header-actions {
  display: flex;
  align-items: center;
  gap: 6px;
}

/* === Body Layout === */
.app-body {
  display: flex;
  flex: 1;
  margin-top: var(--header-height);
  min-height: calc(100vh - var(--header-height));
}

/* === Sidebar === */
.sidebar {
  width: var(--sidebar-width);
  min-width: 200px;
  max-width: 400px;
  flex-shrink: 0;
  background: var(--bg-sidebar);
  border-right: 1px solid var(--border-divider);
  display: flex;
  flex-direction: column;
  position: relative;
  transition: background var(--transition-base), border-color var(--transition-base);
  overflow: hidden;
}

.sidebar-scroll {
  flex: 1;
  overflow-y: auto;
  padding: 16px 0;
}

.sidebar-footer {
  padding: 12px 16px;
  border-top: 1px solid var(--border-divider);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 8px;
}

/* === Drag Handle === */
.drag-handle {
  position: absolute;
  right: 0;
  top: 0;
  bottom: 0;
  width: 4px;
  cursor: col-resize;
  z-index: 10;
  background: transparent;
  transition: background var(--transition-fast);
}
.drag-handle:hover,
.drag-handle.dragging {
  background: var(--brand-primary);
}
.drag-handle::after {
  content: '';
  position: absolute;
  left: 50%;
  top: 50%;
  transform: translate(-50%, -50%);
  width: 2px;
  height: 24px;
  border-radius: 1px;
  background: var(--border-divider);
  opacity: 0;
  transition: opacity var(--transition-fast);
}
.drag-handle:hover::after,
.drag-handle.dragging::after {
  opacity: 1;
}

/* === Main Content === */
.main {
  flex: 1;
  min-width: 0;
  overflow-y: auto;
  background: var(--bg-page);
  transition: background var(--transition-base);
}

.main-inner {
  max-width: 880px;
  margin: 0 auto;
  padding: 32px 40px 64px;
}

/* === Breadcrumb === */
.breadcrumb {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 0.8125rem;
  color: var(--text-tertiary);
  margin-bottom: 20px;
}
.breadcrumb a {
  color: var(--text-tertiary);
}
.breadcrumb a:hover {
  color: var(--brand-primary);
}
.breadcrumb-sep {
  opacity: 0.5;
}
.breadcrumb-current {
  color: var(--text-secondary);
  font-weight: 500;
}

/* === Page Title === */
.page-title {
  margin-bottom: 8px;
}
.page-subtitle {
  color: var(--text-secondary);
  font-size: 0.9375rem;
  margin-bottom: 28px;
}

/* === Content Card (wraps md2card content) === */
.content-card {
  background: var(--bg-card);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-md);
  border: 1px solid var(--border-default);
  overflow: hidden;
  transition: background var(--transition-base), border-color var(--transition-base), box-shadow var(--transition-base);
}

/* === Prev/Next Nav === */
.page-nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-top: 40px;
  padding-top: 24px;
  border-top: 1px solid var(--border-divider);
  gap: 16px;
}
.page-nav-btn {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 12px 18px;
  border-radius: var(--radius-md);
  background: var(--bg-card);
  border: 1px solid var(--border-default);
  color: var(--text-primary);
  font-size: 0.875rem;
  font-weight: 500;
  transition: all var(--transition-fast);
  cursor: pointer;
  flex: 1;
}
.page-nav-btn:hover {
  border-color: var(--brand-primary);
  box-shadow: var(--shadow-sm);
}
.page-nav-btn.prev {
  justify-content: flex-start;
}
.page-nav-btn.next {
  justify-content: flex-end;
}
.page-nav-btn.disabled {
  opacity: 0.4;
  cursor: not-allowed;
  pointer-events: none;
}
.page-nav-label {
  font-size: 0.75rem;
  color: var(--text-tertiary);
  font-weight: 400;
}
.page-nav-title {
  color: var(--text-primary);
  font-weight: 600;
}

/* === Mobile Sidebar Toggle === */
.sidebar-toggle {
  display: none;
  width: 36px;
  height: 36px;
  align-items: center;
  justify-content: center;
  border-radius: var(--radius-sm);
  background: transparent;
  border: 1px solid var(--border-default);
  color: var(--text-secondary);
  cursor: pointer;
  transition: all var(--transition-fast);
}
.sidebar-toggle:hover {
  background: var(--bg-hover);
  color: var(--text-primary);
}

/* === Mobile Overlay === */
.sidebar-overlay {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,0.3);
  z-index: 90;
  backdrop-filter: blur(2px);
}

/* === Responsive === */
@media (max-width: 1023px) {
  .sidebar {
    position: fixed;
    left: 0;
    top: var(--header-height);
    bottom: 0;
    z-index: 95;
    transform: translateX(-100%);
    transition: transform 0.3s cubic-bezier(0.4, 0, 0.2, 1), background var(--transition-base);
    box-shadow: var(--shadow-lg);
  }
  .sidebar.open {
    transform: translateX(0);
  }
  .sidebar-overlay.show {
    display: block;
  }
  .sidebar-toggle {
    display: flex;
  }
  .drag-handle {
    display: none;
  }
  .main-inner {
    padding: 24px 20px 48px;
  }
}

@media (max-width: 639px) {
  .header {
    padding: 0 16px;
  }
  .header-logo-text {
    display: none;
  }
  .main-inner {
    padding: 20px 16px 40px;
  }
  .page-nav {
    flex-direction: column;
  }
  .page-nav-btn {
    width: 100%;
  }
}