/* ==========================================================================
   单词卡片 —— 现代高级质感样式表
   高质感现代轻量美学：极光光晕背景、通透毛玻璃、精致双层阴影、3D 翻转卡片与流畅微交互
   ========================================================================== */

/* ---------- 设计变量 ---------- */
:root {
  /* 品牌与基底色彩（明朗通透的轻科技风格） */
  --color-bg: #f8fafc;
  --color-surface: rgba(255, 255, 255, 0.92);
  --color-surface-2: #ffffff;
  --color-surface-3: #f1f5f9;
  --color-text: #0f172a;
  --color-text-2: #334155;
  --color-text-3: #64748b;
  --color-muted: #64748b;
  --color-muted-strong: #334155;
  --color-border: rgba(226, 232, 240, 0.85);
  --color-border-subtle: rgba(241, 245, 249, 0.9);

  /* 主题色系（高饱和度灵动蓝紫光） */
  --color-primary: #6366f1;
  --color-primary-strong: #4f46e5;
  --color-primary-soft: rgba(99, 102, 241, 0.1);
  --color-focus: #818cf8;
  --color-focus-soft: rgba(99, 102, 241, 0.25);
  --color-on-primary: #ffffff;

  /* 状态与评分色系 */
  --color-danger: #f43f5e;
  --color-danger-strong: #e11d48;
  --color-danger-soft: rgba(244, 63, 94, 0.1);
  --color-on-danger: #ffffff;

  --color-warn: #f59e0b;
  --color-warn-strong: #d97706;
  --color-warn-soft: rgba(245, 158, 11, 0.1);
  --color-warn-border: rgba(245, 158, 11, 0.35);
  --color-warn-hover-bg: #d97706;
  --color-on-warn: #ffffff;

  --color-success: #10b981;
  --color-success-strong: #059669;
  --color-success-soft: rgba(16, 185, 129, 0.1);

  --color-easy: #06b6d4;
  --color-easy-strong: #0891b2;
  --color-easy-soft: rgba(6, 182, 212, 0.1);

  /* 间距节奏 */
  --space-3xs: 2px;
  --space-2xs: 4px;
  --space-xs: 6px;
  --space-sm: 8px;
  --space-md: 12px;
  --space-lg: 16px;
  --space-xl: 24px;
  --space-2xl: 32px;

  /* 字号 / 行高 */
  --font-xs: 0.75rem;
  --font-sm: 0.84rem;
  --font-md: 0.92rem;
  --font-base: 1rem;
  --font-lg: 1.15rem;
  --font-xl: 1.38rem;
  --font-2xl: 1.85rem;
  --leading-tight: 1.24;
  --leading-snug: 1.42;
  --leading-normal: 1.5;
  --leading-relaxed: 1.65;
  --tracking-wide: 0.015em;

  /* 形状 */
  --radius-xs: 6px;
  --radius-sm: 10px;
  --radius: 16px;
  --radius-lg: 22px;
  --radius-pill: 999px;

  /* 多层级软质投影 */
  --shadow-card: 0 10px 28px -4px rgba(15, 23, 42, 0.05), 0 2px 8px -2px rgba(15, 23, 42, 0.03);
  --shadow-toast: 0 16px 36px -4px rgba(15, 23, 42, 0.2);
  --shadow-lift: 0 16px 32px -4px rgba(99, 102, 241, 0.16), 0 4px 10px -2px rgba(15, 23, 42, 0.04);
  --shadow-focus: 0 0 0 4px var(--color-focus-soft);

  /* 动效缓动 */
  --duration-fast: 120ms;
  --duration: 200ms;
  --duration-flip: 260ms;
  --ease: cubic-bezier(0.2, 0.8, 0.2, 1);
  --ease-out: cubic-bezier(0.16, 1, 0.3, 1);
  --spring-ease: cubic-bezier(0.34, 1.3, 0.64, 1);

  /* 触控目标高度 */
  --tap: 44px;
}

/* 兼容暗色环境（降级支持） */
:root[data-theme="dark"] {
  --color-bg: #0f172a;
  --color-surface: rgba(30, 41, 59, 0.92);
  --color-surface-2: #1e293b;
  --color-surface-3: #334155;
  --color-text: #f8fafc;
  --color-text-2: #cbd5e1;
  --color-text-3: #94a3b8;
  --color-border: rgba(51, 65, 85, 0.85);
  --color-primary: #818cf8;
  --color-primary-strong: #a5b4fc;
  --shadow-card: 0 12px 30px rgba(0, 0, 0, 0.4);
}

/* ---------- 基础重置 ---------- */
*,
*::before,
*::after {
  box-sizing: border-box;
}

html,
body {
  margin: 0;
  padding: 0;
}

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

body {
  min-height: 100vh;
  padding: var(--space-lg) var(--space-md) var(--space-2xl);
  color: var(--color-text);
  background-color: var(--color-bg);
  background-image:
    radial-gradient(circle at 10% 12%, rgba(99, 102, 241, 0.09) 0%, transparent 45%),
    radial-gradient(circle at 90% 88%, rgba(236, 72, 153, 0.07) 0%, transparent 45%),
    radial-gradient(circle at 50% 50%, rgba(59, 130, 246, 0.04) 0%, transparent 65%);
  background-attachment: fixed;
  background-repeat: no-repeat;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", "PingFang SC", "Noto Sans SC", sans-serif;
  line-height: var(--leading-normal);
  word-break: break-word;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

/* 屏幕阅读器专用 */
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0 0 0 0);
  clip-path: inset(50%);
  white-space: nowrap;
  border: 0;
}

/* ---------- 页面框架 ---------- */
.app {
  width: 100%;
  max-width: 860px;
  margin: 0 auto;
  display: flex;
  flex-direction: column;
  gap: var(--space-lg);
}

/* 顶部导航毛玻璃胶囊 */
.app__header {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-md);
  padding: 10px 18px;
  background: rgba(255, 255, 255, 0.85);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-pill);
  box-shadow: 0 4px 18px -2px rgba(15, 23, 42, 0.04);
}

.app__title {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  margin: 0;
  font-size: var(--font-xl);
  font-weight: 800;
  line-height: var(--leading-tight);
  letter-spacing: -0.01em;
  background: linear-gradient(135deg, #0f172a 0%, #4338ca 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}

.app__title-icon {
  color: var(--color-primary);
  flex-shrink: 0;
}

.app__nav {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--space-xs);
}

.nav-link {
  display: inline-flex;
  align-items: center;
  min-height: 38px;
  padding: 6px 16px;
  font-size: var(--font-md);
  font-weight: 600;
  color: var(--color-text-2);
  text-decoration: none;
  border-radius: var(--radius-pill);
  transition: all var(--duration) var(--ease);
}

.nav-link:hover {
  background: rgba(99, 102, 241, 0.08);
  color: var(--color-primary-strong);
  transform: translateY(-1px);
}

.nav-link.is-active {
  color: #ffffff;
  background: linear-gradient(135deg, var(--color-primary) 0%, var(--color-primary-strong) 100%);
  box-shadow: 0 4px 14px rgba(99, 102, 241, 0.35);
}

/* 视图容器与平滑进场过渡 */
.view {
  display: flex;
  flex-direction: column;
  gap: var(--space-lg);
}

.view-enter {
  animation: view-fade-up 260ms var(--ease-out) both;
}

@keyframes view-fade-up {
  from {
    opacity: 0;
    transform: translateY(10px);
  }
  to {
    opacity: 1;
    transform: none;
  }
}

/* 通用毛玻璃卡片面板 */
.panel {
  background: var(--color-surface);
  backdrop-filter: blur(14px);
  -webkit-backdrop-filter: blur(14px);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-card);
  padding: var(--space-xl);
  position: relative;
  transition: border-color var(--duration) var(--ease);
}

.panel__title {
  margin: 0 0 var(--space-md);
  font-size: var(--font-lg);
  font-weight: 700;
  letter-spacing: -0.01em;
  line-height: var(--leading-snug);
  color: var(--color-text);
}

.panel__head {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-md);
  margin-bottom: var(--space-md);
}

.panel__head .panel__title {
  margin: 0;
}

.row {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-sm);
  align-items: center;
}

.row--end {
  justify-content: flex-end;
}

.spacer {
  flex: 1 1 auto;
}

/* ---------- 按钮系统 ---------- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-xs);
  min-height: var(--tap);
  padding: 9px var(--space-lg);
  font: inherit;
  font-size: var(--font-md);
  font-weight: 600;
  line-height: 1.2;
  text-align: center;
  color: var(--color-text);
  background: #ffffff;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  box-shadow: 0 2px 4px rgba(15, 23, 42, 0.02);
  cursor: pointer;
  text-decoration: none;
  position: relative;
  transition: all var(--duration) var(--ease);
}

.btn:hover:not(:disabled):not([aria-disabled="true"]) {
  border-color: rgba(99, 102, 241, 0.5);
  color: var(--color-primary-strong);
  background: rgba(99, 102, 241, 0.05);
  transform: translateY(-2px);
  box-shadow: 0 6px 14px -2px rgba(15, 23, 42, 0.08);
}

.btn:active:not(:disabled) {
  transform: scale(0.97) translateY(0);
}

.btn:disabled {
  opacity: 0.45;
  cursor: not-allowed;
  transform: none !important;
  box-shadow: none !important;
}

.btn--primary {
  color: var(--color-on-primary);
  background: linear-gradient(135deg, var(--color-primary) 0%, var(--color-primary-strong) 100%);
  border-color: transparent;
  box-shadow: 0 4px 14px rgba(99, 102, 241, 0.35);
}

.btn--primary:hover:not(:disabled) {
  color: var(--color-on-primary);
  background: linear-gradient(135deg, #4f46e5 0%, #4338ca 100%);
  box-shadow: 0 8px 20px rgba(99, 102, 241, 0.45);
}

.btn--danger {
  color: var(--color-danger-strong);
  background: var(--color-danger-soft);
  border-color: transparent;
}

.btn--danger:hover:not(:disabled) {
  color: var(--color-on-danger);
  background: var(--color-danger-strong);
  border-color: var(--color-danger-strong);
  box-shadow: 0 4px 14px rgba(244, 63, 94, 0.3);
}

.btn--ghost {
  background: transparent;
  border-color: transparent;
  color: var(--color-text-2);
  box-shadow: none;
}

.btn--ghost:hover:not(:disabled) {
  background: var(--color-surface-3);
  border-color: var(--color-border);
  color: var(--color-text);
}

.btn[aria-pressed="true"] {
  color: var(--color-primary-strong);
  background: var(--color-primary-soft);
  border-color: var(--color-primary);
}

.btn--small {
  min-height: 38px;
  padding: 6px var(--space-md);
  font-size: var(--font-sm);
  border-radius: var(--radius-sm);
}

.btn--icon {
  min-width: 38px;
  padding: 6px var(--space-sm);
}

/* 朗读单词声波扩散动效 */
.btn.is-speaking {
  animation: soundwave 0.9s infinite ease-in-out;
  border-color: var(--color-primary);
  color: var(--color-primary-strong);
}

@keyframes soundwave {
  0%, 100% {
    transform: scale(1);
    box-shadow: 0 0 0 0 rgba(99, 102, 241, 0.45);
  }
  50% {
    transform: scale(1.04);
    box-shadow: 0 0 0 8px rgba(99, 102, 241, 0);
  }
}

/* ---------- 表单控件 ---------- */
.field {
  display: flex;
  flex-direction: column;
  gap: var(--space-2xs);
}

.field--full {
  grid-column: 1 / -1;
}

.field__label {
  font-size: var(--font-sm);
  font-weight: 600;
  color: var(--color-text-2);
}

.input,
.textarea {
  width: 100%;
  padding: 10px var(--space-md);
  font: inherit;
  font-size: var(--font-base);
  color: var(--color-text);
  background: #ffffff;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  box-shadow: inset 0 1px 2px rgba(15, 23, 42, 0.03);
  transition: all var(--duration) var(--ease);
}

.input:focus,
.textarea:focus {
  outline: none;
  border-color: var(--color-primary);
  box-shadow: var(--shadow-focus);
}

.textarea {
  min-height: 120px;
  resize: vertical;
  line-height: var(--leading-relaxed);
}

.form-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--space-md);
}

.form-actions {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--space-sm);
  margin-top: var(--space-md);
}

.form-error {
  margin: 0;
  font-size: var(--font-sm);
  font-weight: 600;
  color: var(--color-danger);
}

.hint {
  margin: var(--space-xs) 0 0;
  font-size: var(--font-sm);
  color: var(--color-text-3);
  line-height: var(--leading-relaxed);
}

/* ---------- 概览区域 ---------- */
.overview {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-md);
  align-items: center;
  justify-content: space-between;
}

.overview__text {
  margin: 0;
  font-size: var(--font-lg);
  font-weight: 700;
  line-height: var(--leading-snug);
  letter-spacing: -0.01em;
}

.overview__hint {
  margin: var(--space-xs) 0 0;
  font-size: var(--font-sm);
  color: var(--color-text-3);
}

/* ---------- 列表与交错入场动画 ---------- */
.deck-list,
.card-list,
.stat-list {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  gap: var(--space-sm);
}

.deck {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--space-md);
  padding: var(--space-lg);
  background: #ffffff;
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  box-shadow: 0 2px 6px rgba(15, 23, 42, 0.02);
  animation: item-cascade 280ms var(--ease-out) both;
  animation-delay: calc(var(--i, 0) * 35ms);
  transition: all var(--duration) var(--ease);
}

.deck:hover,
.deck:focus-within {
  border-color: rgba(99, 102, 241, 0.4);
  transform: translateY(-2px);
  box-shadow: var(--shadow-lift);
}

.deck__main {
  flex: 1 1 200px;
  min-width: 0;
}

.deck__name {
  margin: 0;
  font-size: var(--font-base);
  font-weight: 700;
  line-height: var(--leading-snug);
  overflow-wrap: anywhere;
}

.deck__meta {
  margin: var(--space-2xs) 0 0;
  font-size: var(--font-sm);
  color: var(--color-text-3);
}

.deck__actions {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-xs);
}

/* ---------- 徽标与标签 ---------- */
.badge {
  display: inline-flex;
  align-items: center;
  padding: 2px 10px;
  font-size: var(--font-xs);
  font-weight: 600;
  line-height: var(--leading-snug);
  color: var(--color-text-2);
  background: var(--color-surface-3);
  border-radius: var(--radius-pill);
}

.badge--new {
  color: var(--color-primary-strong);
  background: var(--color-primary-soft);
  border: 1px solid rgba(99, 102, 241, 0.2);
}

.badge--due {
  color: var(--color-warn-strong);
  background: var(--color-warn-soft);
  border: 1px solid rgba(245, 158, 11, 0.2);
}

.tags {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2xs);
  margin-top: var(--space-xs);
}

.tag {
  padding: 2px 9px;
  font-size: var(--font-xs);
  font-weight: 600;
  line-height: var(--leading-snug);
  color: var(--color-primary-strong);
  background: rgba(99, 102, 241, 0.08);
  border-radius: var(--radius-pill);
  transition: background-color var(--duration) var(--ease);
}

.tag:hover {
  background: rgba(99, 102, 241, 0.16);
}

/* ---------- 卡片列表项 ---------- */
.card-item {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-md);
  align-items: flex-start;
  padding: var(--space-lg);
  background: #ffffff;
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  box-shadow: 0 2px 6px rgba(15, 23, 42, 0.02);
  animation: item-cascade 280ms var(--ease-out) both;
  animation-delay: calc(var(--i, 0) * 35ms);
  transition: all var(--duration) var(--ease);
}

.card-item:hover,
.card-item:focus-within {
  border-color: rgba(99, 102, 241, 0.4);
  transform: translateY(-2px);
  box-shadow: var(--shadow-lift);
}

@keyframes item-cascade {
  from {
    opacity: 0;
    transform: translateY(12px) scale(0.985);
  }
  to {
    opacity: 1;
    transform: none;
  }
}

.card-item__main {
  flex: 1 1 220px;
  min-width: 0;
}

.card-item__front {
  margin: 0;
  font-size: var(--font-lg);
  font-weight: 700;
  line-height: var(--leading-tight);
  letter-spacing: -0.01em;
  color: var(--color-text);
  overflow-wrap: anywhere;
}

.card-item__back {
  margin: var(--space-xs) 0 0;
  font-size: var(--font-base);
  color: var(--color-text-2);
  overflow-wrap: anywhere;
}

.card-item__example {
  margin: var(--space-sm) 0 0;
  padding-left: var(--space-sm);
  font-size: var(--font-md);
  line-height: var(--leading-snug);
  color: var(--color-text-3);
  border-left: 3px solid rgba(99, 102, 241, 0.3);
  overflow-wrap: anywhere;
}

.card-item__meta {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-xs);
  align-items: center;
  margin-top: var(--space-sm);
}

.card-item__actions {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2xs);
}

/* ---------- 搜索栏 ---------- */
.search-bar {
  display: flex;
  gap: var(--space-sm);
  align-items: center;
  flex-wrap: wrap;
}

.search-bar .input {
  flex: 1 1 200px;
}

/* ---------- 空状态 ---------- */
.empty {
  margin: var(--space-md) 0;
  padding: var(--space-2xl) var(--space-lg);
  text-align: center;
  font-size: var(--font-base);
  color: var(--color-text-3);
  background: var(--color-surface);
  border: 1px dashed var(--color-border);
  border-radius: var(--radius-lg);
}

.empty p {
  margin: 0 0 var(--space-md);
}

.empty .btn {
  margin-top: var(--space-xs);
}

/* ---------- 学习页：3D 翻牌与沉浸交互 ---------- */
.study {
  display: flex;
  flex-direction: column;
  gap: var(--space-lg);
  perspective: 1200px;
}

.study__top {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-sm);
}

.study > .btn {
  align-self: center;
  min-width: 200px;
}

.study__tools {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: center;
  gap: var(--space-md);
}

.study__tools .btn {
  min-width: 170px;
}

.study__counter {
  margin: 0;
  font-size: var(--font-sm);
  color: var(--color-text-3);
  font-variant-numeric: tabular-nums;
  font-weight: 500;
}

.study__top .study__counter + .study__counter {
  font-size: var(--font-md);
  font-weight: 700;
  color: var(--color-text-2);
}

/* 流动光泽进度条 */
.progress {
  height: 12px;
  background: var(--color-surface-3);
  border-radius: var(--radius-pill);
  overflow: hidden;
  box-shadow: inset 0 2px 4px rgba(15, 23, 42, 0.05);
}

.progress__bar {
  height: 100%;
  width: 0;
  background: linear-gradient(90deg, #6366f1, #8b5cf6, #06b6d4);
  border-radius: var(--radius-pill);
  transition: width 380ms var(--spring-ease);
  box-shadow: 0 0 12px rgba(99, 102, 241, 0.45);
}

/* 3D 拟物单词卡片本体 */
.flashcard {
  display: flex;
  flex-direction: column;
  gap: var(--space-md);
  align-items: center;
  justify-content: center;
  min-height: 250px;
  padding: var(--space-2xl) var(--space-lg);
  text-align: center;
  background: linear-gradient(150deg, #ffffff 0%, #f8fafc 100%);
  border: 1px solid rgba(226, 232, 240, 0.95);
  border-radius: var(--radius-lg);
  box-shadow: 0 12px 32px -4px rgba(15, 23, 42, 0.08), 0 4px 10px -2px rgba(15, 23, 42, 0.03);
  cursor: pointer;
  position: relative;
  overflow: hidden;
  transform-style: preserve-3d;
  animation: card-spring-in 300ms var(--spring-ease) both;
  transition: transform 220ms var(--spring-ease),
              box-shadow 220ms var(--ease),
              border-color 220ms var(--ease);
}

.flashcard:hover {
  border-color: rgba(99, 102, 241, 0.5);
  box-shadow: 0 20px 42px -6px rgba(99, 102, 241, 0.18), 0 8px 16px -4px rgba(15, 23, 42, 0.05);
  transform: translateY(-4px) scale(1.008);
}

.flashcard:active {
  transform: scale(0.985) translateY(0);
}

/* 卡片高光扫光 */
.flashcard::after {
  content: '';
  position: absolute;
  top: -60%;
  left: -60%;
  width: 220%;
  height: 220%;
  background: linear-gradient(
    60deg,
    transparent 42%,
    rgba(255, 255, 255, 0.55) 50%,
    transparent 58%
  );
  transform: rotate(25deg) translateY(-100%);
  pointer-events: none;
  transition: transform 700ms var(--ease-out);
}

.flashcard:hover::after {
  transform: rotate(25deg) translateY(100%);
}

.flashcard__front {
  margin: 0;
  max-width: 100%;
  font-size: clamp(2rem, 9.5vw, 2.75rem);
  font-weight: 800;
  line-height: var(--leading-tight);
  letter-spacing: -0.015em;
  color: var(--color-text);
  overflow-wrap: anywhere;
  transition: font-size var(--duration-flip) var(--ease-out), color var(--duration) var(--ease);
}

/* 翻面状态：触发 3D 纵深感微转折 */
.flashcard:has(.flashcard__back),
.flashcard.is-flipped {
  justify-content: flex-start;
  animation: card-flip-3d 320ms var(--spring-ease) both;
}

.flashcard:has(.flashcard__back) .flashcard__front,
.flashcard.is-flipped .flashcard__front {
  font-size: var(--font-lg);
  font-weight: 600;
  color: var(--color-text-2);
}

.flashcard__back {
  width: 100%;
  max-width: 42ch;
  margin: 0;
  padding-top: var(--space-md);
  font-size: 1.35rem;
  font-weight: 700;
  line-height: var(--leading-snug);
  color: var(--color-text);
  border-top: 1px solid rgba(226, 232, 240, 0.8);
  overflow-wrap: anywhere;
  animation: face-reveal 240ms var(--ease-out) both;
}

.flashcard__example {
  width: 100%;
  max-width: 42ch;
  margin: 0;
  font-size: var(--font-md);
  line-height: var(--leading-relaxed);
  color: var(--color-text-3);
  overflow-wrap: anywhere;
  animation: face-reveal 240ms var(--ease-out) 40ms both;
}

.flashcard__hint {
  margin: 0;
  font-size: var(--font-sm);
  color: var(--color-text-3);
  font-weight: 500;
}

@keyframes card-spring-in {
  from {
    opacity: 0;
    transform: translateY(16px) scale(0.94);
  }
  to {
    opacity: 1;
    transform: none;
  }
}

@keyframes card-flip-3d {
  0% {
    transform: rotateX(0deg) scale(1);
  }
  40% {
    transform: rotateX(-30deg) scale(0.975) translateY(-5px);
  }
  100% {
    transform: rotateX(0deg) scale(1);
  }
}

@keyframes face-reveal {
  from {
    opacity: 0;
    transform: translateY(8px);
  }
  to {
    opacity: 1;
    transform: none;
  }
}

/* 兼容旧 keyframe 名称 */
@keyframes flip-in {
  from {
    opacity: 0;
    transform: translateY(8px);
  }
  to {
    opacity: 1;
    transform: none;
  }
}

@keyframes card-turn {
  from {
    transform: rotateX(-12deg);
  }
  to {
    transform: none;
  }
}

/* 四档评分按钮网格与触感反馈 */
.rate-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: var(--space-md);
}

.rate-btn {
  display: flex;
  flex-direction: column;
  gap: var(--space-2xs);
  align-items: center;
  justify-content: center;
  min-height: 64px;
  padding: 12px var(--space-md);
  font: inherit;
  font-size: var(--font-base);
  font-weight: 700;
  color: var(--color-text);
  background: #ffffff;
  border: 1px solid var(--color-border);
  border-left-width: 5px;
  border-radius: var(--radius);
  box-shadow: 0 4px 10px rgba(15, 23, 42, 0.03);
  cursor: pointer;
  position: relative;
  transition: all 180ms var(--ease);
}

.rate-btn--again {
  color: #e11d48;
  background: rgba(244, 63, 94, 0.07);
  border-left-color: #f43f5e;
}

.rate-btn--hard {
  color: #d97706;
  background: rgba(245, 158, 11, 0.07);
  border-left-color: #f59e0b;
}

.rate-btn--good {
  color: #059669;
  background: rgba(16, 185, 129, 0.07);
  border-left-color: #10b981;
}

.rate-btn--easy {
  color: #0284c7;
  background: rgba(6, 182, 212, 0.07);
  border-left-color: #06b6d4;
}

.rate-btn:hover:not(:disabled) {
  transform: translateY(-3px);
}

.rate-btn--again:hover:not(:disabled) {
  border-color: #f43f5e;
  border-left-color: #e11d48;
  box-shadow: 0 8px 22px rgba(244, 63, 94, 0.22);
}

.rate-btn--hard:hover:not(:disabled) {
  border-color: #f59e0b;
  border-left-color: #d97706;
  box-shadow: 0 8px 22px rgba(245, 158, 11, 0.22);
}

.rate-btn--good:hover:not(:disabled) {
  border-color: #10b981;
  border-left-color: #059669;
  box-shadow: 0 8px 22px rgba(16, 185, 129, 0.22);
}

.rate-btn--easy:hover:not(:disabled) {
  border-color: #06b6d4;
  border-left-color: #0284c7;
  box-shadow: 0 8px 22px rgba(6, 182, 212, 0.22);
}

.rate-btn:active:not(:disabled) {
  transform: scale(0.96) translateY(0);
}

.rate-btn:disabled {
  opacity: 0.45;
  cursor: not-allowed;
  transform: none !important;
  box-shadow: none !important;
}

.rate-btn__key {
  display: inline-block;
  padding: 1px 7px;
  font-size: 0.72rem;
  font-weight: 700;
  color: var(--color-text-3);
  background: rgba(255, 255, 255, 0.85);
  border: 1px solid rgba(203, 213, 225, 0.8);
  border-radius: 6px;
  box-shadow: 0 1px 2px rgba(0, 0, 0, 0.04);
  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;
}

/* ---------- 统计页 ---------- */
.stat-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: var(--space-md);
}

.stat {
  padding: var(--space-lg);
  background: #ffffff;
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  box-shadow: 0 2px 6px rgba(15, 23, 42, 0.02);
  transition: all var(--duration) var(--ease);
}

.stat:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-lift);
  border-color: rgba(99, 102, 241, 0.35);
}

.stat__label {
  margin: 0;
  font-size: var(--font-xs);
  font-weight: 700;
  letter-spacing: 0.04em;
  color: var(--color-text-3);
  text-transform: uppercase;
}

/* 连续打卡：通过纯 CSS 徽标脉冲微动效强调，不使用任何 emoji */
.stat:nth-child(4) .stat__label::after {
  content: '';
  display: inline-block;
  width: 7px;
  height: 7px;
  margin-left: 6px;
  background: #f59e0b;
  border-radius: 50%;
  box-shadow: 0 0 0 0 rgba(245, 158, 11, 0.7);
  animation: pulse-dot 1.8s infinite;
  vertical-align: middle;
}

@keyframes pulse-dot {
  0% {
    transform: scale(0.95);
    box-shadow: 0 0 0 0 rgba(245, 158, 11, 0.7);
  }
  70% {
    transform: scale(1.1);
    box-shadow: 0 0 0 6px rgba(245, 158, 11, 0);
  }
  100% {
    transform: scale(0.95);
    box-shadow: 0 0 0 0 rgba(245, 158, 11, 0);
  }
}

.stat__value {
  margin: var(--space-xs) 0 0;
  font-size: var(--font-2xl);
  font-weight: 800;
  line-height: var(--leading-tight);
  letter-spacing: -0.02em;
  font-variant-numeric: tabular-nums;
  color: var(--color-text);
}

.stat__sub {
  margin: var(--space-2xs) 0 0;
  font-size: var(--font-xs);
  line-height: var(--leading-snug);
  color: var(--color-text-3);
}

.bars {
  display: flex;
  flex-direction: column;
  gap: var(--space-md);
}

.bar-row {
  display: grid;
  grid-template-columns: 48px 1fr 40px;
  gap: var(--space-sm);
  align-items: center;
  font-size: var(--font-sm);
}

.bar-row__label {
  color: var(--color-text-3);
  white-space: nowrap;
  font-weight: 500;
}

.bar-track {
  height: 10px;
  background: var(--color-surface-3);
  border-radius: var(--radius-pill);
  overflow: hidden;
  box-shadow: inset 0 1px 3px rgba(15, 23, 42, 0.05);
}

.bar-fill {
  height: 100%;
  min-width: 2px;
  background: linear-gradient(90deg, #6366f1 0%, #a855f7 100%);
  border-radius: var(--radius-pill);
  transition: width 400ms var(--spring-ease);
}

.bar-row__value {
  text-align: right;
  font-weight: 700;
  color: var(--color-text-2);
  font-variant-numeric: tabular-nums;
}

/* ---------- 警告条 ---------- */
.alert {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--space-md);
  padding: var(--space-md) var(--space-lg);
  color: var(--color-warn-strong);
  background: var(--color-warn-soft);
  border: 1px solid var(--color-warn-border);
  border-left: 4px solid var(--color-warn);
  border-radius: var(--radius);
}

.alert[hidden] {
  display: none;
}

.alert__text {
  flex: 1 1 100%;
  margin: 0;
  font-size: var(--font-md);
  font-weight: 600;
  line-height: var(--leading-snug);
  overflow-wrap: anywhere;
}

.alert .btn {
  flex: 0 0 auto;
  color: var(--color-warn-strong);
  background: #ffffff;
  border-color: var(--color-warn-border);
}

.alert .btn:hover:not(:disabled) {
  background: var(--color-warn-hover-bg);
  border-color: var(--color-warn-hover-bg);
  color: var(--color-on-warn);
}

/* ---------- 提示条 ---------- */
.toast {
  position: fixed;
  left: 50%;
  bottom: max(20px, env(safe-area-inset-bottom));
  z-index: 100;
  display: flex;
  align-items: center;
  gap: var(--space-md);
  max-width: calc(100% - 24px);
  padding: 10px var(--space-lg);
  color: #ffffff;
  background: rgba(15, 23, 42, 0.94);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border: 1px solid rgba(255, 255, 255, 0.1);
  border-radius: var(--radius-pill);
  box-shadow: var(--shadow-toast);
  opacity: 0;
  visibility: hidden;
  transform: translate(-50%, 14px) scale(0.96);
  transition: opacity var(--duration) var(--ease),
              transform var(--duration) var(--spring-ease),
              visibility var(--duration) var(--ease);
}

.toast.is-visible {
  opacity: 1;
  visibility: visible;
  transform: translate(-50%, 0) scale(1);
}

.toast__text {
  font-size: var(--font-md);
  font-weight: 500;
  line-height: var(--leading-snug);
  overflow-wrap: anywhere;
}

.toast__undo {
  flex: 0 0 auto;
  min-height: 32px;
  padding: 4px var(--space-md);
  font: inherit;
  font-size: var(--font-sm);
  font-weight: 600;
  color: #a5b4fc;
  background: rgba(255, 255, 255, 0.08);
  border: 1px solid rgba(165, 180, 252, 0.4);
  border-radius: var(--radius-pill);
  cursor: pointer;
  transition: background-color var(--duration) var(--ease);
}

.toast__undo:hover {
  background: rgba(255, 255, 255, 0.2);
}

.toast__undo[hidden] {
  display: none;
}

/* 通关彩花喷射全屏画布 */
.confetti-canvas {
  position: fixed;
  top: 0;
  left: 0;
  width: 100vw;
  height: 100vh;
  pointer-events: none;
  z-index: 9999;
}

/* ---------- 响应式调整 ---------- */
@media (min-width: 640px) {
  body {
    padding: var(--space-2xl) var(--space-xl) 64px;
  }

  .form-grid {
    grid-template-columns: repeat(2, 1fr);
  }

  .rate-grid {
    grid-template-columns: repeat(4, 1fr);
  }

  .stat-grid {
    grid-template-columns: repeat(4, 1fr);
  }
}

/* ---------- 减弱动效适配 (无障碍) ---------- */
@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }

  .flashcard,
  .flashcard:has(.flashcard__back),
  .flashcard.is-flipped {
    animation: none !important;
    transform: none !important;
  }

  .flashcard::after {
    display: none !important;
  }
}