/* ==============================
   期末测验练习 - 样式
   ============================== */

:root {
  --color-primary: #6366f1;
  --color-primary-dark: #4f46e5;
  --color-primary-light: #818cf8;
  --color-accent: #8b5cf6;
  --color-success: #10b981;
  --color-success-bg: #d1fae5;
  --color-error: #ef4444;
  --color-error-bg: #fee2e2;
  --color-warning: #f59e0b;
  --color-warning-bg: #fef3c7;

  --color-bg: #f8fafc;
  --color-surface: #ffffff;
  --color-surface-soft: #f1f5f9;
  --color-border: #e2e8f0;
  --color-border-strong: #cbd5e1;

  --color-text: #0f172a;
  --color-text-soft: #475569;
  --color-text-muted: #94a3b8;

  --shadow-sm: 0 1px 2px rgba(15, 23, 42, 0.05);
  --shadow-md: 0 4px 12px rgba(15, 23, 42, 0.08);
  --shadow-lg: 0 12px 32px rgba(15, 23, 42, 0.12);
  --shadow-xl: 0 24px 60px rgba(99, 102, 241, 0.18);

  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;
  --radius-xl: 22px;

  --gradient-primary: linear-gradient(135deg, #6366f1 0%, #8b5cf6 100%);
  --gradient-primary-soft: linear-gradient(135deg, rgba(99, 102, 241, 0.08), rgba(139, 92, 246, 0.08));

  --transition: 0.2s cubic-bezier(0.4, 0, 0.2, 1);
}

* {
  box-sizing: border-box;
}

html, body {
  margin: 0;
  padding: 0;
  height: 100%;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Microsoft YaHei", "Helvetica Neue", Arial, sans-serif;
  font-size: 15px;
  line-height: 1.6;
  color: var(--color-text);
  background: var(--color-bg);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

button {
  font-family: inherit;
  font-size: inherit;
  cursor: pointer;
  -webkit-appearance: none;
  appearance: none;
  outline: none;
  -webkit-tap-highlight-color: transparent;
}

input, textarea, select {
  font-family: inherit;
  font-size: inherit;
  color: inherit;
}

code, pre {
  font-family: "JetBrains Mono", "Fira Code", Consolas, "Courier New", monospace;
  font-size: 0.92em;
}

code {
  background: var(--color-surface-soft);
  color: #be185d;
  padding: 2px 6px;
  border-radius: 4px;
}

pre {
  background: #0f172a;
  color: #e2e8f0;
  padding: 14px 16px;
  border-radius: var(--radius-md);
  overflow-x: auto;
  margin: 12px 0;
  line-height: 1.5;
}

pre code {
  background: transparent;
  color: inherit;
  padding: 0;
  border-radius: 0;
}

/* ========== Header ========== */
.app-header {
  background: var(--color-surface);
  border-bottom: 1px solid var(--color-border);
  position: sticky;
  top: 0;
  z-index: 50;
  box-shadow: var(--shadow-sm);
}

.app-header__inner {
  max-width: 1400px;
  margin: 0 auto;
  padding: 16px 24px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
  flex-wrap: wrap;
}

.app-brand {
  display: flex;
  align-items: center;
  gap: 14px;
}

.app-brand__icon {
  font-size: 32px;
  line-height: 1;
}

.app-brand__title {
  margin: 0;
  font-size: 20px;
  font-weight: 700;
  background: var(--gradient-primary);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.app-brand__subtitle {
  margin: 2px 0 0;
  font-size: 12px;
  color: var(--color-text-muted);
}

.subject-nav {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
}

.subject-tab {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 10px 18px;
  border: 1px solid var(--color-border);
  background: var(--color-surface);
  border-radius: 999px;
  font-size: 14px;
  font-weight: 500;
  color: var(--color-text-soft);
  transition: var(--transition);
}

.subject-tab:hover:not(.is-disabled) {
  border-color: var(--color-primary-light);
  color: var(--color-primary);
  transform: translateY(-1px);
}

.subject-tab.is-active {
  background: var(--gradient-primary);
  color: white;
  border-color: transparent;
  box-shadow: 0 4px 12px rgba(99, 102, 241, 0.3);
}

.subject-tab.is-disabled {
  opacity: 0.55;
  cursor: not-allowed;
}

.subject-tab__icon {
  font-size: 16px;
}

/* ========== Main Layout ========== */
.app-main {
  max-width: 1400px;
  margin: 0 auto;
  padding: 24px;
  display: grid;
  grid-template-columns: 280px 1fr;
  gap: 24px;
  align-items: start;
}

/* ========== Sidebar ========== */
.app-sidebar {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 20px;
  position: sticky;
  top: 100px;
  max-height: calc(100vh - 120px);
  display: flex;
  flex-direction: column;
  gap: 20px;
  box-shadow: var(--shadow-sm);
}

.sidebar-section {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.sidebar-section--grow {
  flex: 1;
  min-height: 0;
  overflow-y: auto;
}

.sidebar-section--actions {
  border-top: 1px solid var(--color-border);
  padding-top: 16px;
  flex-shrink: 0;
}

.sidebar-section__title {
  margin: 0;
  font-size: 12px;
  font-weight: 600;
  color: var(--color-text-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.subject-summary__hint {
  margin: 0;
  font-size: 13px;
  color: var(--color-text-muted);
}

.subject-summary__name {
  margin: 0 0 4px;
  font-size: 16px;
  font-weight: 600;
  color: var(--color-text);
}

.subject-summary__desc {
  margin: 0 0 8px;
  font-size: 13px;
  color: var(--color-text-soft);
}

.subject-summary__stats {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  margin-top: 6px;
}

.stat-chip {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  padding: 3px 8px;
  background: var(--color-surface-soft);
  border-radius: 6px;
  font-size: 12px;
  color: var(--color-text-soft);
}

.stat-chip__count {
  font-weight: 600;
  color: var(--color-text);
}

/* ========== Type Filter ========== */
.type-filter {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
}

.type-filter__btn {
  padding: 6px 12px;
  border: 1px solid var(--color-border);
  background: var(--color-surface);
  border-radius: 999px;
  font-size: 13px;
  color: var(--color-text-soft);
  transition: var(--transition);
}

.type-filter__btn:hover:not(:disabled) {
  border-color: var(--color-primary-light);
  color: var(--color-primary);
}

.type-filter__btn.is-active {
  background: var(--color-primary);
  color: white;
  border-color: var(--color-primary);
}

.type-filter__btn:disabled {
  opacity: 0.4;
  cursor: not-allowed;
}

/* ========== Question Grid ========== */
.question-grid {
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  gap: 6px;
}

.question-grid__hint {
  grid-column: 1 / -1;
  margin: 0;
  font-size: 13px;
  color: var(--color-text-muted);
}

.q-btn {
  aspect-ratio: 1;
  border: 1px solid var(--color-border);
  background: var(--color-surface);
  border-radius: var(--radius-sm);
  font-size: 13px;
  font-weight: 500;
  color: var(--color-text-soft);
  transition: var(--transition);
  display: flex;
  align-items: center;
  justify-content: center;
}

.q-btn:hover:not(:disabled) {
  border-color: var(--color-primary-light);
  color: var(--color-primary);
}

.q-btn.is-current {
  background: var(--color-primary);
  color: white;
  border-color: var(--color-primary);
}

.q-btn.is-correct {
  background: var(--color-success-bg);
  color: var(--color-success);
  border-color: var(--color-success);
}

.q-btn.is-incorrect {
  background: var(--color-error-bg);
  color: var(--color-error);
  border-color: var(--color-error);
}

.q-btn:disabled {
  opacity: 0.55;
  cursor: not-allowed;
}

/* ========== Buttons ========== */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  padding: 10px 18px;
  border: 1px solid transparent;
  border-radius: var(--radius-md);
  font-size: 14px;
  font-weight: 500;
  transition: var(--transition);
  white-space: nowrap;
}

.btn:focus-visible,
.option:focus-visible,
.q-btn:focus-visible,
.type-filter__btn:focus-visible,
.subject-tab:focus-visible,
.sidebar-toggle:focus-visible,
.mobile-bar__btn:focus-visible,
.assemble-counter__btn:focus-visible,
.wrong-item__go:focus-visible {
  box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.2);
}

.btn:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

.btn--primary {
  background: var(--gradient-primary);
  color: white;
  box-shadow: 0 4px 12px rgba(99, 102, 241, 0.25);
}

.btn--primary:hover:not(:disabled) {
  transform: translateY(-1px);
  box-shadow: 0 6px 16px rgba(99, 102, 241, 0.35);
}

.btn--ghost {
  background: var(--color-surface);
  color: var(--color-text-soft);
  border-color: var(--color-border);
}

.btn--ghost:hover:not(:disabled) {
  border-color: var(--color-primary-light);
  color: var(--color-primary);
}

.btn--accent {
  background: linear-gradient(135deg, #f59e0b 0%, #f97316 100%);
  color: white;
  border-color: transparent;
  box-shadow: 0 4px 12px rgba(245, 158, 11, 0.25);
}

.btn--accent:hover:not(:disabled) {
  transform: translateY(-1px);
  box-shadow: 0 6px 16px rgba(245, 158, 11, 0.35);
}

.btn--small {
  padding: 6px 12px;
  font-size: 13px;
}

.sidebar-section--actions .btn {
  width: 100%;
}

/* ========== Content / Question Card ========== */
.app-content {
  min-width: 0;
}

.question-card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 32px;
  min-height: 480px;
  box-shadow: var(--shadow-sm);
}

.welcome-screen {
  text-align: center;
  padding: 40px 20px;
}

.welcome-screen__icon {
  font-size: 64px;
  margin-bottom: 16px;
}

.welcome-screen__title {
  margin: 0 0 8px;
  font-size: 24px;
  font-weight: 700;
  color: var(--color-text);
}

.welcome-screen__desc {
  margin: 0 0 32px;
  color: var(--color-text-soft);
}

.subject-cards {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(220px, 1fr));
  gap: 16px;
  max-width: 720px;
  margin: 0 auto;
}

.subject-card {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 8px;
  padding: 24px 16px;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  background: var(--color-surface);
  transition: var(--transition);
  text-align: center;
}

.subject-card:hover:not(.is-disabled) {
  border-color: var(--color-primary-light);
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}

.subject-card.is-disabled {
  opacity: 0.55;
  cursor: not-allowed;
}

.subject-card__icon {
  font-size: 36px;
}

.subject-card__name {
  font-size: 16px;
  font-weight: 600;
  color: var(--color-text);
}

.subject-card__meta {
  font-size: 12px;
  color: var(--color-text-muted);
}

.subject-card__badge {
  font-size: 11px;
  padding: 2px 8px;
  background: var(--color-warning-bg);
  color: var(--color-warning);
  border-radius: 999px;
  margin-top: 4px;
}

/* ========== Question Display ========== */
.question {
  animation: fadeIn 0.25s ease;
}

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

.question__header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  flex-wrap: wrap;
  margin-bottom: 16px;
}

.question__meta {
  display: flex;
  align-items: center;
  gap: 8px;
  flex-wrap: wrap;
}

.question__index {
  font-size: 13px;
  color: var(--color-text-muted);
  font-weight: 500;
}

.question__type {
  display: inline-flex;
  align-items: center;
  padding: 3px 10px;
  font-size: 12px;
  font-weight: 500;
  border-radius: 999px;
  background: var(--gradient-primary-soft);
  color: var(--color-primary);
}

.question__type--single { background: rgba(99, 102, 241, 0.1); color: var(--color-primary); }
.question__type--fill { background: rgba(16, 185, 129, 0.1); color: var(--color-success); }
.question__type--judge { background: rgba(245, 158, 11, 0.1); color: var(--color-warning); }
.question__type--short { background: rgba(139, 92, 246, 0.1); color: var(--color-accent); }
.question__type--code { background: rgba(236, 72, 153, 0.1); color: #db2777; }

.question__status {
  font-size: 13px;
  font-weight: 600;
}

.question__status--correct { color: var(--color-success); }
.question__status--incorrect { color: var(--color-error); }
.question__status--unanswered { color: var(--color-text-muted); }

.question__title {
  margin: 0 0 20px;
  font-size: 17px;
  font-weight: 600;
  line-height: 1.6;
  color: var(--color-text);
}

.question__title code,
.question__body code {
  background: var(--color-surface-soft);
  color: #be185d;
  padding: 2px 6px;
  border-radius: 4px;
  font-size: 0.92em;
}

/* ========== Options (Single / Judge) ========== */
.options {
  display: flex;
  flex-direction: column;
  gap: 10px;
  margin-bottom: 20px;
}

.option {
  display: flex;
  align-items: flex-start;
  gap: 12px;
  padding: 12px 16px;
  border: 1.5px solid var(--color-border);
  background: var(--color-surface);
  border-radius: var(--radius-md);
  transition: var(--transition);
  cursor: pointer;
  text-align: left;
  width: 100%;
  color: var(--color-text);
  -webkit-appearance: none;
  appearance: none;
}

.option:hover:not(:disabled) {
  border-color: var(--color-primary-light);
  background: var(--gradient-primary-soft);
}

.option:disabled {
  cursor: default;
}

.option__key {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 28px;
  height: 28px;
  flex-shrink: 0;
  border: 1.5px solid var(--color-border-strong);
  border-radius: 50%;
  font-weight: 600;
  font-size: 13px;
  color: var(--color-text-soft);
  background: var(--color-surface);
  transition: var(--transition);
}

.option__text {
  flex: 1;
  line-height: 1.6;
}

.option__text code {
  background: var(--color-surface-soft);
  color: #be185d;
  padding: 2px 6px;
  border-radius: 4px;
  font-size: 0.92em;
}

.option.is-selected {
  border-color: var(--color-primary);
  background: var(--gradient-primary-soft);
}

.option.is-selected .option__key {
  background: var(--color-primary);
  color: white;
  border-color: var(--color-primary);
}

.option.is-correct {
  border-color: var(--color-success);
  background: var(--color-success-bg);
}

.option.is-correct .option__key {
  background: var(--color-success);
  color: white;
  border-color: var(--color-success);
}

.option.is-wrong {
  border-color: var(--color-error);
  background: var(--color-error-bg);
}

.option.is-wrong .option__key {
  background: var(--color-error);
  color: white;
  border-color: var(--color-error);
}

/* ========== Fill in the Blank ========== */
.fill-inputs {
  display: flex;
  flex-direction: column;
  gap: 12px;
  margin-bottom: 20px;
}

.fill-input-row {
  display: flex;
  align-items: center;
  gap: 10px;
  flex-wrap: wrap;
}

.fill-input-row__label {
  font-size: 13px;
  color: var(--color-text-soft);
  font-weight: 500;
  min-width: 64px;
}

.fill-input {
  flex: 1;
  min-width: 180px;
  padding: 8px 12px;
  border: 1.5px solid var(--color-border);
  border-radius: var(--radius-sm);
  background: var(--color-surface);
  transition: var(--transition);
}

.fill-input:focus {
  outline: none;
  border-color: var(--color-primary);
  box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.15);
}

.fill-input.is-correct {
  border-color: var(--color-success);
  background: var(--color-success-bg);
}

.fill-input.is-wrong {
  border-color: var(--color-error);
  background: var(--color-error-bg);
}

/* ========== Short / Code Answer ========== */
.answer-textarea {
  width: 100%;
  min-height: 120px;
  padding: 12px 14px;
  border: 1.5px solid var(--color-border);
  border-radius: var(--radius-md);
  background: var(--color-surface);
  resize: vertical;
  line-height: 1.6;
  font-family: inherit;
  transition: var(--transition);
}

.answer-textarea--code {
  font-family: "JetBrains Mono", "Fira Code", Consolas, "Courier New", monospace;
  font-size: 14px;
  min-height: 160px;
  background: #0f172a;
  color: #e2e8f0;
  border-color: #1e293b;
}

.answer-textarea:focus {
  outline: none;
  border-color: var(--color-primary);
  box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.15);
}

.answer-actions {
  display: flex;
  gap: 10px;
  align-items: center;
  margin-top: 12px;
  flex-wrap: wrap;
}

.answer-status {
  font-size: 13px;
  color: var(--color-text-soft);
}

/* ========== Feedback / Explanation ========== */
.feedback {
  margin-top: 20px;
  padding: 16px;
  border-radius: var(--radius-md);
  border-left: 4px solid;
  animation: fadeIn 0.3s ease;
}

.feedback--correct {
  background: var(--color-success-bg);
  border-color: var(--color-success);
  color: #065f46;
}

.feedback--incorrect {
  background: var(--color-error-bg);
  border-color: var(--color-error);
  color: #991b1b;
}

.feedback--info {
  background: var(--color-surface-soft);
  border-color: var(--color-primary);
  color: var(--color-text);
}

.feedback__title {
  margin: 0 0 8px;
  font-size: 14px;
  font-weight: 600;
  display: flex;
  align-items: center;
  gap: 6px;
}

.feedback__answer {
  margin: 0 0 8px;
  font-size: 14px;
}

.feedback__explanation {
  margin: 8px 0 0;
  font-size: 14px;
  line-height: 1.7;
}

.feedback__explanation-label {
  font-weight: 600;
  margin-right: 4px;
}

.feedback pre {
  background: rgba(15, 23, 42, 0.85);
  color: #e2e8f0;
  margin: 8px 0 0;
}

/* ========== Question Navigation ========== */
.question-nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-top: 28px;
  padding-top: 20px;
  border-top: 1px solid var(--color-border);
  gap: 12px;
  flex-wrap: wrap;
}

.question-nav__info {
  font-size: 13px;
  color: var(--color-text-muted);
}

.question-nav__buttons {
  display: flex;
  gap: 8px;
}

/* ========== Toast ========== */
.toast {
  position: fixed;
  bottom: 24px;
  left: 50%;
  transform: translateX(-50%) translateY(20px);
  background: var(--color-text);
  color: white;
  padding: 10px 20px;
  border-radius: 999px;
  font-size: 14px;
  box-shadow: var(--shadow-lg);
  opacity: 0;
  transition: transform 0.3s ease, opacity 0.3s ease;
  z-index: 100;
  pointer-events: none;
}

.toast.is-visible {
  transform: translateX(-50%) translateY(0);
  opacity: 1;
}

.toast--success { background: var(--color-success); }
.toast--error { background: var(--color-error); }
.toast--info { background: var(--color-primary); }

/* ========== Modal ========== */
.modal {
  position: fixed;
  inset: 0;
  z-index: 200;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 20px;
}

.modal[hidden] {
  display: none;
}

.modal__backdrop {
  position: absolute;
  inset: 0;
  background: rgba(15, 23, 42, 0.55);
  backdrop-filter: blur(4px);
}

.modal__panel {
  position: relative;
  background: var(--color-surface);
  border-radius: var(--radius-lg);
  width: 100%;
  max-width: 520px;
  max-height: calc(100vh - 40px);
  display: flex;
  flex-direction: column;
  box-shadow: var(--shadow-xl);
  animation: modalIn 0.25s ease;
}

@keyframes modalIn {
  from { opacity: 0; transform: translateY(20px) scale(0.97); }
  to { opacity: 1; transform: translateY(0) scale(1); }
}

.modal__header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 20px 24px;
  border-bottom: 1px solid var(--color-border);
}

.modal__header h2 {
  margin: 0;
  font-size: 18px;
  font-weight: 600;
}

.modal__close {
  width: 32px;
  height: 32px;
  border: none;
  background: transparent;
  font-size: 24px;
  line-height: 1;
  color: var(--color-text-muted);
  border-radius: 50%;
  transition: var(--transition);
}

.modal__close:hover {
  background: var(--color-surface-soft);
  color: var(--color-text);
}

.modal__body {
  padding: 24px;
  overflow-y: auto;
  flex: 1;
}

.modal__footer {
  display: flex;
  justify-content: flex-end;
  gap: 10px;
  padding: 16px 24px;
  border-top: 1px solid var(--color-border);
}

.result-score {
  text-align: center;
  padding: 12px 0 20px;
}

.result-score__circle {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 120px;
  height: 120px;
  border-radius: 50%;
  background: var(--gradient-primary);
  color: white;
  font-size: 32px;
  font-weight: 700;
  box-shadow: var(--shadow-lg);
  position: relative;
}

.result-score__circle--good { background: linear-gradient(135deg, #10b981, #059669); }
.result-score__circle--ok { background: linear-gradient(135deg, #f59e0b, #d97706); }
.result-score__circle--bad { background: linear-gradient(135deg, #ef4444, #dc2626); }

.result-score__label {
  margin-top: 8px;
  font-size: 14px;
  color: var(--color-text-muted);
}

.result-summary {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 10px;
  margin-top: 8px;
}

.result-stat {
  text-align: center;
  padding: 12px;
  border-radius: var(--radius-md);
  background: var(--color-surface-soft);
}

.result-stat__value {
  display: block;
  font-size: 22px;
  font-weight: 700;
}

.result-stat__label {
  font-size: 12px;
  color: var(--color-text-muted);
  margin-top: 2px;
}

.result-stat--correct .result-stat__value { color: var(--color-success); }
.result-stat--incorrect .result-stat__value { color: var(--color-error); }
.result-stat--unanswered .result-stat__value { color: var(--color-text-muted); }

.result-type-list {
  margin-top: 16px;
  display: flex;
  flex-direction: column;
  gap: 6px;
}

.result-type-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 8px 12px;
  background: var(--color-surface-soft);
  border-radius: var(--radius-sm);
  font-size: 13px;
}

.result-type-row__name { color: var(--color-text-soft); }
.result-type-row__score { font-weight: 600; }

/* ========== Mobile Sidebar Toggle ========== */
.sidebar-toggle {
  display: none;
  width: 40px;
  height: 40px;
  border: 1px solid var(--color-border);
  background: var(--color-surface);
  border-radius: var(--radius-sm);
  font-size: 20px;
  color: var(--color-text-soft);
  transition: var(--transition);
  position: relative;
  flex-shrink: 0;
}

.sidebar-toggle:hover {
  border-color: var(--color-primary-light);
  color: var(--color-primary);
}

.sidebar-toggle__badge {
  position: absolute;
  top: -4px;
  right: -4px;
  min-width: 16px;
  height: 16px;
  padding: 0 4px;
  background: var(--color-error);
  color: white;
  font-size: 10px;
  font-weight: 700;
  border-radius: 999px;
  display: flex;
  align-items: center;
  justify-content: center;
}

/* ========== Mobile Bottom Bar ========== */
.mobile-bar {
  display: none;
  position: fixed;
  bottom: 0;
  left: 0;
  right: 0;
  height: 56px;
  background: var(--color-surface);
  border-top: 1px solid var(--color-border);
  box-shadow: 0 -2px 12px rgba(15, 23, 42, 0.06);
  z-index: 60;
  padding: 0 8px;
  align-items: center;
  justify-content: space-around;
  gap: 4px;
  padding-bottom: env(safe-area-inset-bottom, 0);
}

.mobile-bar__btn {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 2px;
  flex: 1;
  height: 100%;
  border: none;
  background: transparent;
  color: var(--color-text-soft);
  font-size: 11px;
  font-weight: 500;
  transition: var(--transition);
  -webkit-tap-highlight-color: transparent;
  cursor: pointer;
  min-width: 0;
  padding: 0 4px;
}

.mobile-bar__btn:active:not(:disabled) {
  background: var(--color-surface-soft);
}

.mobile-bar__btn:disabled {
  opacity: 0.35;
  cursor: not-allowed;
}

.mobile-bar__btn--primary {
  color: var(--color-primary);
  font-weight: 600;
}

.mobile-bar__icon {
  font-size: 18px;
  line-height: 1;
}

.mobile-bar__label {
  line-height: 1;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  max-width: 100%;
}

/* ========== Mobile Types Panel ========== */
.mobile-types {
  display: none;
  position: fixed;
  inset: 0;
  z-index: 80;
}

.mobile-types__backdrop {
  position: absolute;
  inset: 0;
  background: rgba(15, 23, 42, 0.45);
  backdrop-filter: blur(2px);
}

.mobile-types__panel {
  position: absolute;
  bottom: 0;
  left: 0;
  right: 0;
  background: var(--color-surface);
  border-radius: var(--radius-lg) var(--radius-lg) 0 0;
  padding: 0;
  max-height: 50vh;
  overflow-y: auto;
  animation: slideUp 0.25s ease;
}

@keyframes slideUp {
  from { transform: translateY(100%); }
  to { transform: translateY(0); }
}

.mobile-types__header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 16px 20px;
  border-bottom: 1px solid var(--color-border);
  position: sticky;
  top: 0;
  background: var(--color-surface);
  z-index: 1;
}

.mobile-types__header h3 {
  margin: 0;
  font-size: 16px;
  font-weight: 600;
}

.mobile-types__close {
  width: 36px;
  height: 36px;
  border: none;
  background: var(--color-surface-soft);
  border-radius: 50%;
  font-size: 20px;
  color: var(--color-text-soft);
  display: flex;
  align-items: center;
  justify-content: center;
}

.mobile-types__body {
  padding: 12px 16px 20px;
  display: flex;
  flex-direction: column;
  gap: 6px;
  padding-bottom: calc(20px + env(safe-area-inset-bottom, 0));
}

.mobile-type-btn {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 14px 16px;
  border: 1px solid var(--color-border);
  background: var(--color-surface);
  border-radius: var(--radius-md);
  font-size: 15px;
  font-weight: 500;
  color: var(--color-text);
  transition: var(--transition);
  -webkit-tap-highlight-color: transparent;
  cursor: pointer;
}

.mobile-type-btn:active {
  background: var(--color-surface-soft);
}

.mobile-type-btn.is-active {
  background: var(--gradient-primary);
  color: white;
  border-color: transparent;
}

.mobile-type-btn__count {
  font-size: 12px;
  color: var(--color-text-muted);
  background: var(--color-surface-soft);
  padding: 2px 8px;
  border-radius: 999px;
}

.mobile-type-btn.is-active .mobile-type-btn__count {
  background: rgba(255, 255, 255, 0.2);
  color: rgba(255, 255, 255, 0.9);
}

/* ========== Assemble Form ========== */
.assemble-hint {
  margin: 0 0 16px;
  font-size: 14px;
  color: var(--color-text-soft);
  line-height: 1.5;
}

.assemble-form {
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.assemble-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  padding: 10px 14px;
  background: var(--color-surface-soft);
  border-radius: var(--radius-md);
}

.assemble-row__left {
  display: flex;
  align-items: center;
  gap: 10px;
}

.assemble-row__icon {
  font-size: 18px;
  width: 32px;
  text-align: center;
}

.assemble-row__label {
  font-size: 14px;
  font-weight: 500;
  color: var(--color-text);
}

.assemble-row__max {
  font-size: 12px;
  color: var(--color-text-muted);
  margin-left: 4px;
}

.assemble-row__right {
  display: flex;
  align-items: center;
  gap: 6px;
}

.assemble-counter {
  display: inline-flex;
  align-items: center;
  gap: 0;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  overflow: hidden;
  background: var(--color-surface);
}

.assemble-counter__btn {
  width: 32px;
  height: 32px;
  border: none;
  background: var(--color-surface);
  color: var(--color-text-soft);
  font-size: 18px;
  font-weight: 600;
  cursor: pointer;
  transition: var(--transition);
  display: flex;
  align-items: center;
  justify-content: center;
}

.assemble-counter__btn:hover:not(:disabled) {
  background: var(--color-surface-soft);
  color: var(--color-primary);
}

.assemble-counter__btn:disabled {
  opacity: 0.35;
  cursor: not-allowed;
}

.assemble-counter__value {
  width: 36px;
  text-align: center;
  font-size: 15px;
  font-weight: 600;
  color: var(--color-text);
  border-left: 1px solid var(--color-border);
  border-right: 1px solid var(--color-border);
  padding: 4px 0;
}

.assemble-total {
  margin-top: 12px;
  padding: 10px 14px;
  background: var(--gradient-primary-soft);
  border-radius: var(--radius-md);
  text-align: center;
  font-size: 14px;
  font-weight: 600;
  color: var(--color-primary);
}

/* ========== Scrollbar ========== */
.app-sidebar::-webkit-scrollbar,
.modal__body::-webkit-scrollbar {
  width: 6px;
}

.app-sidebar::-webkit-scrollbar-thumb,
.modal__body::-webkit-scrollbar-thumb {
  background: var(--color-border-strong);
  border-radius: 3px;
}

/* ========== Responsive ========== */
@media (max-width: 960px) {
  .app-main {
    grid-template-columns: 1fr;
  }

  .app-sidebar {
    position: static;
    max-height: none;
  }

  .question-grid {
    grid-template-columns: repeat(8, 1fr);
  }
}

@media (max-width: 640px) {
  /* -- Header -- */
  .app-header__inner {
    padding: 10px 12px;
    gap: 10px;
  }

  .app-brand__icon {
    font-size: 26px;
  }

  .app-brand__title {
    font-size: 16px;
  }

  .app-brand__subtitle {
    display: none;
  }

  .subject-nav {
    display: none;           /* 手机端隐藏顶部学科切换，改用欢迎卡片 */
  }

  .sidebar-toggle {
    display: flex;
  }

  /* -- Main layout: 单列，底部留出 mobile-bar 空间 -- */
  .app-main {
    padding: 12px;
    padding-bottom: 72px;   /* 56px bar + 16px spacing */
    gap: 0;
  }

  /* -- Sidebar: 手机端默认隐藏，改为浮层 -- */
  .app-sidebar {
    display: none;
    position: fixed;
    top: 0;
    left: 0;
    bottom: 56px;
    width: 85vw;
    max-width: 320px;
    z-index: 70;
    border-radius: 0;
    border: none;
    box-shadow: 4px 0 24px rgba(15, 23, 42, 0.15);
    animation: slideInLeft 0.25s ease;
    padding-bottom: env(safe-area-inset-bottom, 0);
  }

  .app-sidebar.is-open {
    display: flex;
  }

  @keyframes slideInLeft {
    from { transform: translateX(-100%); }
    to   { transform: translateX(0); }
  }

  /* 侧边栏遮罩 */
  .sidebar-overlay {
    display: none;
    position: fixed;
    inset: 0;
    background: rgba(15, 23, 42, 0.4);
    z-index: 65;
  }

  .sidebar-overlay.is-visible {
    display: block;
  }

  .sidebar-section--actions {
    flex-direction: column;
    gap: 8px;
    padding-top: 12px;
    padding-bottom: 12px;
  }

  .sidebar-section--actions .btn {
    width: 100%;
    padding: 12px 16px;
    font-size: 15px;
  }

  /* -- Question Card -- */
  .question-card {
    padding: 16px;
    min-height: auto;
    border-radius: var(--radius-md);
  }

  .question__title {
    font-size: 15px;
    line-height: 1.7;
    margin-bottom: 16px;
  }

  /* -- Options: 更大的触摸目标 -- */
  .option {
    padding: 14px 12px;
    gap: 10px;
    min-height: 48px;
  }

  .option__key {
    width: 32px;
    height: 32px;
    font-size: 14px;
    flex-shrink: 0;
  }

  .option__text {
    font-size: 14px;
    line-height: 1.5;
  }

  /* -- Fill inputs -- */
  .fill-input-row {
    flex-direction: column;
    align-items: stretch;
    gap: 4px;
  }

  .fill-input-row__label {
    min-width: auto;
    font-size: 12px;
    color: var(--color-text-muted);
  }

  .fill-input {
    padding: 12px;
    font-size: 15px;
    min-height: 44px;
  }

  /* -- Textarea -- */
  .answer-textarea {
    min-height: 100px;
    padding: 12px;
    font-size: 14px;
  }

  .answer-textarea--code {
    min-height: 140px;
    font-size: 13px;
  }

  /* -- Question nav: 隐藏桌面端导航，改用底部栏 -- */
  .question-nav {
    display: none;
  }

  /* -- Question grid: 隐藏侧边栏内的网格 -- */
  .question-grid {
    grid-template-columns: repeat(6, 1fr);
    gap: 4px;
  }

  .q-btn {
    font-size: 12px;
    border-radius: 4px;
  }

  /* -- Welcome screen -- */
  .welcome-screen {
    padding: 24px 12px;
  }

  .welcome-screen__icon {
    font-size: 48px;
    margin-bottom: 12px;
  }

  .welcome-screen__title {
    font-size: 20px;
  }

  .welcome-screen__desc {
    font-size: 14px;
    margin-bottom: 24px;
  }

  .subject-cards {
    grid-template-columns: repeat(2, 1fr);
    gap: 12px;
  }

  .subject-card {
    padding: 18px 12px;
  }

  .subject-card__icon {
    font-size: 28px;
  }

  .subject-card__name {
    font-size: 14px;
  }

  /* -- Feedback -- */
  .feedback {
    padding: 12px;
    margin-top: 16px;
  }

  .feedback__title {
    font-size: 13px;
  }

  .feedback__explanation {
    font-size: 13px;
  }

  /* -- Modal -- */
  .modal {
    padding: 0;
    align-items: flex-end;
  }

  .modal__panel {
    max-width: 100%;
    border-radius: var(--radius-lg) var(--radius-lg) 0 0;
    max-height: 85vh;
    padding-bottom: env(safe-area-inset-bottom, 0);
  }

  .modal__header {
    padding: 16px 20px;
  }

  .modal__body {
    padding: 16px 20px;
  }

  .modal__footer {
    padding: 12px 20px;
    padding-bottom: calc(12px + env(safe-area-inset-bottom, 0));
  }

  .result-score__circle {
    width: 100px;
    height: 100px;
    font-size: 28px;
  }

  .result-summary {
    grid-template-columns: 1fr;
    gap: 8px;
  }

  /* -- Assemble form -- */
  .assemble-row {
    padding: 10px 12px;
  }

  .assemble-row__left {
    gap: 8px;
  }

  .assemble-counter__btn {
    width: 36px;
    height: 36px;
    font-size: 20px;
  }

  /* -- Toast -- */
  .toast {
    bottom: 72px;
    left: 50%;
    max-width: calc(100vw - 32px);
    text-align: center;
    font-size: 13px;
    padding: 8px 16px;
  }
}