:root {
  /* ===== Color Tokens ===== */
  --color-primary: #2563EB;
  --color-primary-dark: #1D4ED8;
  --color-primary-light: #DBEAFE;
  --color-primary-tint: #EFF6FF;
  --color-bg: #F8FAFC;
  --color-surface: #FFFFFF;
  --color-surface-subtle: #F1F5F9;
  --color-text: #0F172A;
  --color-text-secondary: #475569;
  --color-text-tertiary: #94A3B8;
  --color-border: #E2E8F0;
  --color-border-light: #F1F5F9;
  --color-success: #16A34A;
  --color-success-light: #DCFCE7;
  --color-warning: #D97706;
  --color-warning-light: #FEF3C7;
  --color-danger: #DC2626;
  --color-danger-light: #FEE2E2;
  --color-overlay: rgba(15, 23, 42, 0.35);

  /* ===== Typography Scale ===== */
  --font-sans: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI",
    "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
  --font-mono: ui-monospace, SFMono-Regular, "Cascadia Code", Consolas, monospace;

  --text-xs: 11px;
  --text-sm: 12px;
  --text-base: 13px;
  --text-body: 14px;
  --text-md: 15px;
  --text-lg: 18px;
  --text-xl: 22px;
  --text-2xl: 28px;

  /* ===== Spacing Scale ===== */
  --space-1: 4px;
  --space-2: 8px;
  --space-3: 12px;
  --space-4: 16px;
  --space-5: 20px;
  --space-6: 24px;
  --space-8: 32px;

  /* ===== Radius ===== */
  --radius-sm: 4px;   /* small: buttons, tags, inputs */
  --radius-md: 8px;   /* medium: cards, panels */
  --radius-lg: 12px;  /* large: modals, large cards */
  /* legacy aliases */
  --radius: var(--radius-sm);
  --radius-xl: var(--radius-lg);

  /* ===== Elevation (minimal) ===== */
  --shadow-sm: 0 1px 2px rgba(0,0,0,0.03);
  --shadow: 0 1px 3px rgba(0,0,0,0.04);
  --shadow-lg: 0 4px 16px rgba(0,0,0,0.06);
  --shadow-xl: 0 8px 32px rgba(0,0,0,0.08);

  /* ===== Motion Tokens ===== */
  --duration-fast: 120ms;
  --duration-normal: 200ms;
  --duration-slow: 300ms;
  --ease-out: cubic-bezier(0.16, 1, 0.3, 1);
  --ease-in-out: cubic-bezier(0.4, 0, 0.2, 1);
  --ease-spring: cubic-bezier(0.34, 1.56, 0.64, 1);

  --transition: var(--duration-normal) var(--ease-out);
  --transition-fast: var(--duration-fast) var(--ease-out);
  --transition-slow: var(--duration-slow) var(--ease-out);

  /* ===== Layout ===== */
  --nav-height: 56px;
  --mobile-header-height: 42px;
  --bottom-nav-height: 56px;
  --bottom-nav-safe: calc(var(--bottom-nav-height) + env(safe-area-inset-bottom, 0px));
  --max-width: 1200px;
}

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

html {
  font-size: 16px;
  -webkit-text-size-adjust: 100%;
}

body {
  font-family: var(--font-sans);
  background: var(--color-bg);
  color: var(--color-text);
  line-height: 1.5;
  min-height: 100vh;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

a { color: inherit; text-decoration: none; }
button { font-family: inherit; cursor: pointer; border: none; background: none; }
ul, ol { list-style: none; }
input, select { font-family: inherit; }

.mono { font-family: var(--font-mono); font-variant-numeric: tabular-nums; }

/* ===== Numeric / value helpers ===== */
.stat-num,
.value,
.number,
.mono,
.time-value,
.countdown-value,
.countdown-sec,
.freetime-value,
.ft-now-value,
.load-stat-value,
.stat-inline-value,
.sch-stat-num,
.data-info-value,
.progress-item-value,
.semester-week-num,
.semester-week-total,
.free-time-chip-value,
.m-empty-stat-num {
  white-space: nowrap;
  font-variant-numeric: tabular-nums;
}

/* ===== Global overflow protection ===== */
/* Grid and flex children need min-width: 0 to allow shrinking below content size */
.grid > *,
.flex-col > * {
  min-width: 0;
}

.app-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: var(--color-surface);
  border-bottom: 1px solid var(--color-border);
  height: var(--nav-height);
}

.app-header-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 24px;
  gap: 16px;
}

.header-left {
  display: flex;
  align-items: center;
  gap: 20px;
  flex-shrink: 0;
}

.class-selector {
  position: relative;
}

.class-selector-btn {
  display: flex;
  align-items: center;
  gap: 6px;
  font-size: 15px;
  font-weight: 600;
  color: var(--color-text);
  padding: 6px 12px;
  border-radius: var(--radius-sm);
  transition: background var(--transition-fast);
}

.class-selector-btn:hover {
  background: var(--color-primary-tint);
}

.class-selector-btn .chevron {
  width: 16px;
  height: 16px;
  color: var(--color-text-secondary);
  transition: transform var(--transition);
}

.class-selector-btn.open .chevron {
  transform: rotate(180deg);
}

.class-selector-dropdown {
  position: absolute;
  top: calc(100% + 4px);
  left: 0;
  min-width: 240px;
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  box-shadow: var(--shadow-lg);
  padding: 6px;
  opacity: 0;
  visibility: hidden;
  transform: translateY(-4px);
  transition: opacity var(--transition-fast), transform var(--transition-fast), visibility var(--transition-fast);
}

.class-selector-dropdown.open {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}

.class-option {
  display: flex;
  align-items: center;
  gap: 8px;
  width: 100%;
  padding: 10px 12px;
  border-radius: var(--radius-sm);
  font-size: 14px;
  color: var(--color-text);
  transition: background var(--transition-fast);
  text-align: left;
}

.class-option:hover { background: var(--color-primary-tint); }

.class-option .check {
  width: 16px;
  height: 16px;
  color: var(--color-primary);
  visibility: hidden;
}

.class-option.active .check { visibility: visible; }

.main-nav {
  display: flex;
  align-items: center;
  gap: 2px;
}

.nav-item {
  font-size: var(--text-base);
  font-weight: 500;
  color: var(--color-text-secondary);
  padding: 8px 16px;
  border-radius: var(--radius-sm);
  letter-spacing: 0.03em;
  transition: color var(--transition-fast), background var(--transition-fast);
  white-space: nowrap;
  position: relative;
}

.nav-item:hover { color: var(--color-text); }
.nav-item.active { color: var(--color-primary); font-weight: 600; }
.nav-item.active::after {
  content: '';
  position: absolute;
  bottom: -1px;
  left: 16px;
  right: 16px;
  height: 2px;
  background: var(--color-primary);
  border-radius: 1px;
}

.nav-item:focus-visible {
  outline: 2px solid var(--color-primary);
  outline-offset: 2px;
  border-radius: var(--radius-sm);
}

.page-container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 24px;
}

.page-view { display: none; }
.page-view.active {
  display: block;
  animation: pageEnter var(--duration-normal) var(--ease-out);
}

@keyframes pageEnter {
  from { opacity: 0; transform: translateY(4px); }
  to { opacity: 1; transform: translateY(0); }
}

.card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  box-shadow: none;
  min-width: 0;
}

.card-pad { padding: 24px; }

.section-title {
  font-size: var(--text-sm);
  font-weight: 600;
  color: var(--color-text-secondary);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 16px;
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  font-size: var(--text-body);
  font-weight: 500;
  padding: 8px 16px;
  border-radius: var(--radius-sm);
  border: 1px solid var(--color-border);
  background: var(--color-surface);
  color: var(--color-text);
  transition: border-color var(--transition-fast), color var(--transition-fast), background var(--transition-fast);
}

.btn:hover { border-color: var(--color-primary); color: var(--color-primary); }
.btn:active { transform: scale(0.98); }
.btn:focus-visible { outline: 2px solid var(--color-primary); outline-offset: 2px; }

.btn-primary {
  background: var(--color-primary);
  color: #fff;
  border-color: var(--color-primary);
}

.btn-primary:hover { background: var(--color-primary-dark); border-color: var(--color-primary-dark); color: #fff; }

.btn-icon {
  width: 36px;
  height: 36px;
  padding: 0;
  display: inline-flex;
  align-items: center;
  justify-content: center;
}

.badge {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  font-size: var(--text-sm);
  font-weight: 600;
  padding: 2px 8px;
  border-radius: var(--radius-sm);
  letter-spacing: 0.02em;
}

.badge-primary { background: var(--color-primary-light); color: var(--color-primary-dark); }
.badge-success { background: var(--color-success-light); color: var(--color-success); }
.badge-warning { background: var(--color-warning-light); color: var(--color-warning); }
.badge-muted { background: var(--color-border-light); color: var(--color-text-secondary); }

.progress-bar {
  width: 100%;
  height: 8px;
  background: var(--color-border-light);
  border-radius: 4px;
  overflow: hidden;
}

.progress-bar-fill {
  height: 100%;
  background: var(--color-primary);
  border-radius: 4px;
  transition: width 300ms ease;
}

.tag {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  font-size: 12px;
  color: var(--color-text-secondary);
  background: var(--color-border-light);
  padding: 2px 8px;
  border-radius: 4px;
}

.empty-state {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 48px 24px;
  text-align: center;
  color: var(--color-text-secondary);
}

.empty-state-icon {
  width: 48px;
  height: 48px;
  color: var(--color-text-tertiary);
  margin-bottom: 12px;
}

.empty-state-text { font-size: 15px; }
.empty-state-sub { font-size: 13px; color: var(--color-text-tertiary); margin-top: 4px; }

.error-banner {
  background: var(--color-danger-light);
  border: 1px solid #FCA5A5;
  color: #991B1B;
  padding: 16px 20px;
  border-radius: var(--radius);
  font-size: 14px;
  margin-bottom: 16px;
}

.detail-overlay {
  position: fixed;
  inset: 0;
  background: var(--color-overlay);
  z-index: 200;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 24px;
  opacity: 0;
  visibility: hidden;
  transition: opacity var(--transition), visibility var(--transition);
}

.detail-overlay.open { opacity: 1; visibility: visible; }

.detail-panel {
  background: var(--color-surface);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-lg);
  width: 100%;
  max-width: 480px;
  max-height: 90vh;
  overflow-y: auto;
  transform: scale(0.96);
  transition: transform var(--transition);
}

.detail-overlay.open .detail-panel { transform: scale(1); }

.detail-header {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  padding: 24px 24px 0;
}

.detail-close {
  width: 32px;
  height: 32px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: var(--radius-sm);
  color: var(--color-text-secondary);
  transition: background var(--transition-fast);
  flex-shrink: 0;
}

.detail-close:hover { background: var(--color-border-light); color: var(--color-text); }

.detail-body { padding: 16px 24px 24px; }

.detail-row {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  padding: 10px 0;
  border-bottom: 1px solid var(--color-border-light);
}

.detail-row:last-child { border-bottom: none; }

.detail-label {
  font-size: 13px;
  color: var(--color-text-secondary);
  flex-shrink: 0;
  width: 80px;
}

.detail-value {
  font-size: 14px;
  color: var(--color-text);
  text-align: right;
  font-weight: 500;
}

.detail-value.muted { color: var(--color-text-tertiary); font-weight: 400; }

.loading-screen {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  min-height: 100vh;
  gap: 16px;
}

.loading-spinner {
  width: 32px;
  height: 32px;
  border: 3px solid var(--color-border);
  border-top-color: var(--color-primary);
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
}

@keyframes spin { to { transform: rotate(360deg); } }

.loading-text { font-size: 14px; color: var(--color-text-secondary); }

.skeleton {
  background: linear-gradient(90deg, var(--color-border-light) 25%, var(--color-border) 50%, var(--color-border-light) 75%);
  background-size: 200% 100%;
  animation: shimmer 1.5s infinite;
  border-radius: var(--radius-sm);
}

@keyframes shimmer { to { background-position: -200% 0; } }

.tooltip {
  position: absolute;
  background: var(--color-text);
  color: #fff;
  font-size: 12px;
  padding: 4px 8px;
  border-radius: 4px;
  pointer-events: none;
  white-space: nowrap;
  z-index: 300;
  opacity: 0;
  transition: opacity var(--transition-fast);
}

.fade-in { animation: fadeIn var(--transition) ease; }
@keyframes fadeIn { from { opacity: 0; } to { opacity: 1; } }

.fade-in-up { animation: fadeInUp var(--transition) ease; }
@keyframes fadeInUp { from { opacity: 0; transform: translateY(8px); } to { opacity: 1; transform: translateY(0); } }

/* ===== Responsive visibility helpers ===== */
.desktop-only { display: block; }
.mobile-only { display: none !important; }

@media (max-width: 768px) {
  .desktop-only { display: none !important; }
  .mobile-only { display: block !important; }
  .bottom-nav.mobile-only { display: flex !important; }
  .mobile-class-dropdown.mobile-only { display: flex !important; }
}

/* ===== Global defensive styles ===== */
html, body {
  max-width: 100%;
  overflow-x: hidden;
}

body {
  padding-top: env(safe-area-inset-top, 0px);
}

img, svg, video, canvas {
  max-width: 100%;
  height: auto;
}

* {
  -webkit-tap-highlight-color: transparent;
}

/* ===== Mobile Header ===== */
.mobile-header {
  position: sticky;
  top: 0;
  z-index: 150;
  background: var(--color-surface);
  border-bottom: 1px solid var(--color-border);
  height: var(--mobile-header-height);
  padding-top: env(safe-area-inset-top, 0px);
}

.mobile-header-inner {
  height: var(--mobile-header-height);
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 0 16px;
  position: relative;
}

.mobile-class-selector {
  position: static;
}

.mobile-class-btn {
  display: flex;
  align-items: center;
  gap: 4px;
  font-size: 14px;
  font-weight: 600;
  color: var(--color-text);
  padding: 4px 8px;
  border-radius: var(--radius-sm);
  min-height: 36px;
  max-width: 200px;
  transition: background var(--transition-fast);
}

.mobile-class-name {
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.mobile-class-btn:active { background: var(--color-primary-tint); }

.mobile-class-btn .chevron {
  width: 14px;
  height: 14px;
  color: var(--color-text-secondary);
  transition: transform var(--transition);
}

.mobile-class-btn.open .chevron {
  transform: rotate(180deg);
}

.mobile-class-dropdown {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: rgba(15, 23, 42, 0.4);
  z-index: 200;
  opacity: 0;
  visibility: hidden;
  transition: opacity var(--transition-fast), visibility var(--transition-fast);
  display: flex;
  align-items: flex-end;
}

.mobile-class-dropdown.open {
  opacity: 1;
  visibility: visible;
}

.mobile-class-dropdown-inner {
  width: 100%;
  background: var(--color-surface);
  border-radius: var(--radius-xl) var(--radius-xl) 0 0;
  padding: 20px 16px calc(20px + var(--bottom-nav-height) + env(safe-area-inset-bottom, 0px));
  max-height: 75vh;
  overflow-y: auto;
  transform: translateY(100%);
  transition: transform var(--transition-slow);
}

.mobile-class-dropdown.open .mobile-class-dropdown-inner {
  transform: translateY(0);
}

.mobile-class-dropdown-title {
  font-size: 13px;
  font-weight: 600;
  color: var(--color-text-secondary);
  text-transform: uppercase;
  letter-spacing: 0.06em;
  margin-bottom: 12px;
  text-align: center;
}

.mobile-class-option {
  display: flex;
  align-items: center;
  gap: 10px;
  width: 100%;
  padding: 10px 14px;
  border-radius: var(--radius);
  font-size: 15px;
  font-weight: 500;
  color: var(--color-text);
  transition: background var(--transition-fast);
  text-align: left;
  min-height: 44px;
}

.mobile-class-option:active { background: var(--color-primary-tint); }

.mobile-class-option.active {
  background: var(--color-primary-tint);
  color: var(--color-primary);
  font-weight: 600;
}

.mobile-class-option .check {
  width: 20px;
  height: 20px;
  color: var(--color-primary);
  flex-shrink: 0;
  visibility: hidden;
}

.mobile-class-option.active .check { visibility: visible; }

/* ===== Bottom Navigation ===== */
.bottom-nav {
  position: fixed;
  bottom: 0;
  left: 0;
  right: 0;
  background: var(--color-surface);
  border-top: 1px solid var(--color-border);
  display: flex;
  align-items: stretch;
  height: var(--bottom-nav-height);
  padding-bottom: env(safe-area-inset-bottom, 0px);
  z-index: 100;
}

.bottom-nav-item {
  flex: 1;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 1px;
  color: var(--color-text-tertiary);
  font-size: 9px;
  font-weight: 500;
  padding: 4px 2px;
  transition: color var(--transition-fast);
  min-height: 44px;
  position: relative;
}

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

.bottom-nav-item.active::before {
  content: '';
  position: absolute;
  top: 0;
  left: 50%;
  transform: translateX(-50%);
  width: 20px;
  height: 2px;
  background: var(--color-primary);
  border-radius: 0 0 1px 1px;
  animation: navIndicatorEnter var(--duration-fast) var(--ease-out);
}

@keyframes navIndicatorEnter {
  from { transform: translateX(-50%) scaleX(0); }
  to { transform: translateX(-50%) scaleX(1); }
}

.bottom-nav-item:active { opacity: 0.6; }
.bottom-nav-item:focus-visible { outline: 2px solid var(--color-primary); outline-offset: -2px; }

.bottom-nav-icon {
  width: 22px;
  height: 22px;
  flex-shrink: 0;
}

.bottom-nav-label {
  font-size: 9px;
  line-height: 1.2;
  letter-spacing: 0.01em;
}

/* ===== Course Card text overflow ===== */
.line-clamp-2 {
  display: -webkit-box;
  -webkit-line-clamp: 2;
  -webkit-box-orient: vertical;
  overflow: hidden;
  text-overflow: ellipsis;
}

/* ===== Table scrollable containers ===== */
.table-scroll {
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
  -ms-overflow-style: -ms-autohiding-scrollbar;
  max-width: 100%;
}

.table-scroll table {
  min-width: 100%;
  width: 100%;
}

/* Sticky table headers */
.sticky-table thead th {
  position: sticky;
  top: 0;
  background: var(--color-surface);
  z-index: 2;
  box-shadow: inset 0 -1px 0 var(--color-border);
}

.sticky-table thead th::after {
  content: '';
  position: absolute;
  left: 0;
  right: 0;
  bottom: -1px;
  height: 1px;
  background: var(--color-border);
}

/* Sticky first column (add .sticky-first-col to enable) */
.sticky-table.sticky-first-col th:first-child,
.sticky-table.sticky-first-col td:first-child {
  position: sticky;
  left: 0;
  z-index: 1;
  background: var(--color-surface);
  box-shadow: 1px 0 0 var(--color-border);
}

.sticky-table.sticky-first-col thead th:first-child {
  z-index: 4;
  box-shadow: 1px 0 0 var(--color-border), inset 0 -1px 0 var(--color-border);
}

/* ===== Bottom Sheet / Modal ===== */
@media (max-width: 768px) {
  .detail-overlay {
    align-items: flex-end;
    justify-content: center;
    padding: 0;
  }

  .detail-panel {
    max-width: 100%;
    max-height: 85vh;
    border-radius: var(--radius-xl) var(--radius-xl) 0 0;
    transform: translateY(100%);
    width: 100%;
    transition: transform var(--duration-slow) var(--ease-out);
    padding-bottom: env(safe-area-inset-bottom, 0px);
    overscroll-behavior: contain;
    -webkit-overflow-scrolling: touch;
    touch-action: pan-y;
  }

  .detail-overlay.open .detail-panel {
    transform: translateY(0);
  }

  .detail-header {
    padding-top: 12px;
    position: relative;
  }

  .detail-header::before {
    content: '';
    position: absolute;
    top: 8px;
    left: 50%;
    transform: translateX(-50%);
    width: 36px;
    height: 4px;
    background: var(--color-border);
    border-radius: 2px;
  }
}

/* ===== Loading / Error / Empty ===== */
.error-state {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 48px 24px;
  text-align: center;
  gap: 12px;
}

.error-state-icon {
  width: 48px;
  height: 48px;
  color: var(--color-danger);
  margin-bottom: 4px;
}

.error-state-title {
  font-size: 16px;
  font-weight: 600;
  color: var(--color-text);
}

.error-state-desc {
  font-size: 14px;
  color: var(--color-text-secondary);
  line-height: 1.5;
}