/* ==========================================================================
   AI · NLP 训练营 — 落地页样式
   组织方式：1 令牌 → 2 基础 → 3 工具类 → 4 组件 → 5 断点 → 6 偏好与打印
   移动优先：所有基础样式面向小屏，宽屏能力通过 min-width 断点叠加
   ========================================================================== */

/* ---------- 1. 设计令牌 ---------- */
:root {
  /* 颜色 */
  --bg:            #08090f;
  --bg-alt:        #0c0e16;
  --surface:       #12141f;
  --surface-2:     #171a26;
  --border:        rgba(255, 255, 255, .08);
  --border-strong: rgba(255, 255, 255, .16);

  --text:          #eceef6;
  --text-muted:    #9ba1b6;
  --text-dim:      #7d849b;

  --primary:       #7c6cff;
  --primary-soft:  rgba(124, 108, 255, .14);
  --secondary:     #22d3ee;
  --grad:          linear-gradient(135deg, #7c6cff 0%, #22d3ee 100%);
  --ok:            #34d399;
  --danger:        #f87171;

  /* 尺寸 */
  --radius-sm: 10px;
  --radius:    16px;
  --radius-lg: 24px;
  --container: 1140px;
  --narrow:    760px;
  --header-h:  64px;

  /* 阴影 */
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, .4);
  --shadow:    0 12px 32px -12px rgba(0, 0, 0, .7);
  --shadow-lg: 0 32px 64px -24px rgba(0, 0, 0, .85);
  --glow:      0 0 0 1px rgba(124, 108, 255, .25), 0 18px 48px -18px rgba(124, 108, 255, .5);

  /* 排版 */
  --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC",
               "Hiragino Sans GB", "Microsoft YaHei", "Helvetica Neue", Helvetica, Arial, sans-serif;
  --font-mono: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas,
               "Liberation Mono", monospace;

  /* 动效 */
  --ease: cubic-bezier(.22, .61, .36, 1);
}

/* ---------- 2. 基础与重置 ---------- */
*,
*::before,
*::after { box-sizing: border-box; }

html {
  scroll-behavior: smooth;
  /* 锚点跳转时给吸顶导航留出空间 */
  scroll-padding-top: calc(var(--header-h) + 16px);
  -webkit-text-size-adjust: 100%;
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: var(--font-sans);
  font-size: 16px;
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  overflow-x: hidden;
}

h1, h2, h3, h4 {
  margin: 0;
  line-height: 1.25;
  letter-spacing: -.02em;
  font-weight: 700;
}

p { margin: 0; }

a {
  color: inherit;
  text-decoration: none;
}

img, svg { display: block; max-width: 100%; }

ul, ol { margin: 0; padding: 0; list-style: none; }

button, input, select, textarea {
  font: inherit;
  color: inherit;
}

/* 键盘可达性：只对键盘操作显示焦点环 */
:focus-visible {
  outline: 2px solid var(--secondary);
  outline-offset: 3px;
  border-radius: 4px;
}

/* 跳过导航（仅在获得焦点时可见） */
.skip-link {
  position: absolute;
  left: 12px;
  top: -100px;
  z-index: 200;
  padding: 10px 18px;
  background: var(--primary);
  color: #fff;
  border-radius: 0 0 var(--radius-sm) var(--radius-sm);
  transition: top .2s var(--ease);
}
.skip-link:focus { top: 0; }

/* ---------- 3. 工具类 ---------- */
.container {
  width: 100%;
  max-width: var(--container);
  margin-inline: auto;
  padding-inline: 20px;
}
.container--narrow { max-width: var(--narrow); }

.section { padding-block: 64px; }
.section--alt { background: var(--bg-alt); }

.section__head {
  max-width: 640px;
  margin-bottom: 40px;
}
.section__title { font-size: clamp(1.6rem, 4.4vw, 2.4rem); }
.section__lead {
  margin-top: 14px;
  color: var(--text-muted);
  font-size: 1.02rem;
}

.eyebrow {
  display: inline-block;
  margin-bottom: 12px;
  color: var(--secondary);
  font-size: .8rem;
  font-weight: 600;
  letter-spacing: .14em;
  text-transform: uppercase;
}

.grad-text {
  background: var(--grad);
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
}

/* ---------- 4. 组件 ---------- */

/* 4.1 按钮 */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 12px 22px;
  border: 1px solid transparent;
  border-radius: 999px;
  background: transparent;
  font-size: .95rem;
  font-weight: 600;
  cursor: pointer;
  white-space: nowrap;
  transition: transform .2s var(--ease), box-shadow .25s var(--ease),
              background-color .25s var(--ease), border-color .25s var(--ease);
}
.btn:active { transform: translateY(1px); }

.btn--primary {
  background: var(--grad);
  color: #0b0c14;
  box-shadow: var(--glow);
}
.btn--primary:hover { filter: brightness(1.08); }

.btn--ghost {
  border-color: var(--border-strong);
  color: var(--text);
  background: rgba(255, 255, 255, .03);
}
.btn--ghost:hover {
  border-color: var(--primary);
  background: var(--primary-soft);
}

.btn--sm  { padding: 9px 16px; font-size: .875rem; }
.btn--lg  { padding: 15px 30px; font-size: 1rem; }
.btn--block { width: 100%; }

.btn__icon { transition: transform .25s var(--ease); }
.btn:hover .btn__icon { transform: translateX(3px); }

/* 4.2 徽标 / 标签 */
.badge {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  margin: 0 0 20px;
  padding: 6px 14px;
  border: 1px solid var(--border-strong);
  border-radius: 999px;
  background: rgba(255, 255, 255, .04);
  color: var(--text-muted);
  font-size: .82rem;
}
.badge__dot {
  width: 7px;
  height: 7px;
  border-radius: 50%;
  background: var(--ok);
  box-shadow: 0 0 0 4px rgba(52, 211, 153, .18);
}

.chip-list {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: 20px;
}
.chip {
  padding: 5px 13px;
  border: 1px solid var(--border);
  border-radius: 999px;
  background: var(--surface);
  color: var(--text-muted);
  font-size: .82rem;
}

/* 4.3 顶部导航 */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(8, 9, 15, .72);
  backdrop-filter: saturate(180%) blur(14px);
  -webkit-backdrop-filter: saturate(180%) blur(14px);
  border-bottom: 1px solid transparent;
  transition: border-color .3s var(--ease), box-shadow .3s var(--ease);
}
.site-header.is-scrolled {
  border-bottom-color: var(--border);
  box-shadow: 0 8px 28px -18px rgba(0, 0, 0, .9);
}

.header__inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  min-height: var(--header-h);
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  font-weight: 700;
  letter-spacing: -.01em;
}
.brand__mark { color: var(--primary); }
.brand__text { font-size: 1rem; }

/* 汉堡按钮 */
.nav-toggle {
  display: inline-flex;
  flex-direction: column;
  justify-content: center;
  gap: 5px;
  width: 42px;
  height: 42px;
  padding: 0 10px;
  border: 1px solid var(--border-strong);
  border-radius: var(--radius-sm);
  background: rgba(255, 255, 255, .03);
  cursor: pointer;
}
.nav-toggle__bar {
  display: block;
  height: 2px;
  border-radius: 2px;
  background: var(--text);
  transition: transform .25s var(--ease), opacity .2s var(--ease);
}
.nav-toggle[aria-expanded="true"] .nav-toggle__bar:nth-child(1) { transform: translateY(7px) rotate(45deg); }
.nav-toggle[aria-expanded="true"] .nav-toggle__bar:nth-child(2) { opacity: 0; }
.nav-toggle[aria-expanded="true"] .nav-toggle__bar:nth-child(3) { transform: translateY(-7px) rotate(-45deg); }

/* 移动端：折叠面板 */
.primary-nav {
  position: absolute;
  left: 0;
  right: 0;
  top: 100%;
  display: none;
  flex-direction: column;
  gap: 4px;
  padding: 14px 20px 22px;
  background: var(--bg-alt);
  border-bottom: 1px solid var(--border);
  box-shadow: var(--shadow);
}
.primary-nav.is-open { display: flex; }

.primary-nav__list { display: flex; flex-direction: column; }
.primary-nav__list a {
  display: block;
  padding: 12px 4px;
  color: var(--text-muted);
  font-size: .95rem;
  border-bottom: 1px solid var(--border);
  transition: color .2s var(--ease);
}
.primary-nav__list a:hover,
.primary-nav__list a.is-active { color: var(--text); }
.primary-nav__cta { margin-top: 16px; align-self: flex-start; }

/* 4.4 Hero 首屏 */
.hero {
  position: relative;
  padding-block: 48px 56px;
  overflow: hidden;
}
.hero__glow {
  position: absolute;
  inset: -30% -10% auto -10%;
  height: 620px;
  pointer-events: none;
  background:
    radial-gradient(46% 52% at 22% 34%, rgba(124, 108, 255, .28), transparent 70%),
    radial-gradient(40% 46% at 78% 12%, rgba(34, 211, 238, .18), transparent 70%);
  filter: blur(20px);
}

.hero__inner {
  position: relative;
  display: grid;
  gap: 40px;
  align-items: center;
}

.hero__title {
  margin-bottom: 20px;
  font-size: clamp(2rem, 7.4vw, 3.5rem);
  letter-spacing: -.03em;
}
.hero__title .grad-text { display: block; }

.hero__lead {
  max-width: 34em;
  color: var(--text-muted);
  font-size: clamp(1rem, 2.6vw, 1.12rem);
}

.hero__actions {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  margin-top: 28px;
}

.hero__meta {
  margin-top: 16px;
  color: var(--text-dim);
  font-size: .88rem;
}

/* 倒计时 */
.countdown { margin-top: 30px; }
.countdown__label {
  margin-bottom: 10px;
  color: var(--text-dim);
  font-size: .82rem;
  letter-spacing: .06em;
}
.countdown__grid {
  display: flex;
  gap: 10px;
  flex-wrap: wrap;
}
.countdown__cell {
  display: flex;
  flex-direction: column;
  align-items: center;
  min-width: 62px;
  padding: 10px 12px;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  background: var(--surface);
}
.countdown__cell strong {
  font-family: var(--font-mono);
  font-size: 1.3rem;
  font-variant-numeric: tabular-nums;
  background: var(--grad);
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
}
.countdown__cell span {
  color: var(--text-dim);
  font-size: .7rem;
  letter-spacing: .08em;
}

/* 代码窗口 */
.hero__visual { position: relative; }
.codewin {
  border: 1px solid var(--border-strong);
  border-radius: var(--radius);
  background: linear-gradient(180deg, #101220 0%, #0b0d16 100%);
  box-shadow: var(--shadow-lg);
  overflow: hidden;
}
.codewin__bar {
  display: flex;
  align-items: center;
  gap: 7px;
  padding: 12px 16px;
  border-bottom: 1px solid var(--border);
  background: rgba(255, 255, 255, .02);
}
.codewin__dot {
  width: 10px;
  height: 10px;
  border-radius: 50%;
}
.codewin__dot--r { background: #ff5f57; }
.codewin__dot--y { background: #febc2e; }
.codewin__dot--g { background: #28c840; }
.codewin__file {
  margin-left: 8px;
  color: var(--text-dim);
  font-family: var(--font-mono);
  font-size: .78rem;
}
.codewin__code {
  margin: 0;
  padding: 18px 16px;
  overflow-x: auto;
  font-family: var(--font-mono);
  font-size: .76rem;
  line-height: 1.85;
  color: #cdd3e4;
  tab-size: 4;
}
.codewin__foot {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  padding: 12px 16px;
  border-top: 1px solid var(--border);
  background: rgba(255, 255, 255, .02);
}
.codewin__tag {
  padding: 3px 10px;
  border: 1px solid var(--border);
  border-radius: 999px;
  color: var(--text-dim);
  font-family: var(--font-mono);
  font-size: .7rem;
}
.codewin__tag--ok { color: var(--ok); border-color: rgba(52, 211, 153, .3); }

/* 语法高亮配色 */
.tk-kw  { color: #c084fc; }
.tk-cls { color: #7dd3fc; }
.tk-fn  { color: #86efac; }
.tk-num { color: #fbbf24; }
.tk-op  { color: #94a3b8; }
.tk-cm  { color: #6b7280; font-style: italic; }

/* 数据条 */
.stats {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 1px;
  margin-top: 52px;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--border);
  overflow: hidden;
}
.stat {
  padding: 20px 18px;
  background: var(--bg);
  text-align: center;
}
.stat strong {
  display: block;
  font-size: 1.6rem;
  letter-spacing: -.02em;
}
.stat span {
  color: var(--text-dim);
  font-size: .84rem;
}

/* 4.5 卡片网格 */
.card-grid {
  display: grid;
  gap: 16px;
  grid-template-columns: 1fr;
}

.card {
  padding: 26px 22px;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--surface);
  transition: transform .3s var(--ease), border-color .3s var(--ease), background-color .3s var(--ease);
}
.card:hover {
  transform: translateY(-4px);
  border-color: var(--border-strong);
  background: var(--surface-2);
}
.card__icon {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 44px;
  height: 44px;
  margin-bottom: 18px;
  border-radius: 12px;
  background: var(--primary-soft);
  color: var(--primary);
}
.card__title {
  margin-bottom: 10px;
  font-size: 1.06rem;
}
.card__text {
  color: var(--text-muted);
  font-size: .92rem;
}

/* 4.6 手风琴（原生 details，无 JS 亦可展开） */
.accordion {
  display: grid;
  gap: 12px;
}

.acc-item {
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--surface);
  overflow: hidden;
  transition: border-color .3s var(--ease);
}
.acc-item[open] { border-color: var(--border-strong); }

.acc-item__head {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 18px 20px;
  cursor: pointer;
  list-style: none;
}
.acc-item__head::-webkit-details-marker { display: none; }
.acc-item__head:hover .acc-item__title { color: var(--secondary); }

.acc-item__week {
  flex-shrink: 0;
  padding: 3px 10px;
  border: 1px solid rgba(124, 108, 255, .3);
  border-radius: 999px;
  background: var(--primary-soft);
  color: var(--primary);
  font-size: .72rem;
  font-weight: 600;
  letter-spacing: .04em;
}
.acc-item__title {
  flex: 1;
  font-size: 1rem;
  font-weight: 600;
  transition: color .2s var(--ease);
}
.acc-item__chev {
  flex-shrink: 0;
  width: 9px;
  height: 9px;
  border-right: 2px solid var(--text-dim);
  border-bottom: 2px solid var(--text-dim);
  transform: rotate(45deg);
  transition: transform .3s var(--ease);
}
.acc-item[open] .acc-item__chev { transform: rotate(-135deg); }

.acc-item__body {
  padding: 0 20px 20px;
  color: var(--text-muted);
  font-size: .92rem;
}
.acc-item__body > p + .tick-list { margin-top: 12px; }

.acc-item__project {
  margin-top: 14px;
  padding: 10px 14px;
  border-left: 3px solid var(--primary);
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  background: rgba(124, 108, 255, .07);
  color: var(--text);
  font-size: .88rem;
}

/* 打勾列表 */
.tick-list { display: grid; gap: 9px; }
.tick-list li {
  position: relative;
  padding-left: 24px;
}
.tick-list li::before {
  content: "";
  position: absolute;
  left: 0;
  top: .55em;
  width: 6px;
  height: 10px;
  border-right: 2px solid var(--ok);
  border-bottom: 2px solid var(--ok);
  transform: rotate(42deg) translateY(-2px);
}
.tick-list--sm { font-size: .9rem; gap: 11px; }

/* 4.7 讲师 */
.instructor {
  display: grid;
  gap: 28px;
  padding: 30px 24px;
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  background:
    radial-gradient(80% 120% at 100% 0%, rgba(124, 108, 255, .12), transparent 60%),
    var(--surface);
}
.instructor__avatar {
  display: grid;
  place-items: center;
  width: 108px;
  height: 108px;
  border-radius: 50%;
  background: var(--grad);
  color: #0b0c14;
  font-size: 2.6rem;
  font-weight: 700;
  box-shadow: var(--glow);
}
.instructor__text {
  margin-top: 14px;
  color: var(--text-muted);
  font-size: .96rem;
}
.instructor__quote {
  margin: 22px 0 0;
  padding: 16px 18px;
  border-left: 3px solid var(--secondary);
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  background: rgba(34, 211, 238, .06);
  color: var(--text);
  font-size: .94rem;
}

/* 4.8 学员评价 */
.quote-grid {
  display: grid;
  gap: 16px;
  grid-template-columns: 1fr;
}
.quote {
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  gap: 20px;
  padding: 24px 22px;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--surface);
}
.quote__text {
  color: var(--text);
  font-size: .95rem;
}
.quote__foot {
  display: flex;
  align-items: center;
  gap: 12px;
}
.quote__avatar {
  display: grid;
  place-items: center;
  width: 40px;
  height: 40px;
  flex-shrink: 0;
  border-radius: 50%;
  background: var(--primary-soft);
  color: var(--primary);
  font-weight: 700;
}
.quote__foot strong { display: block; font-size: .9rem; }
.quote__foot small { color: var(--text-dim); font-size: .8rem; }

/* 4.9 价格 */
.price-grid {
  display: grid;
  gap: 18px;
  grid-template-columns: 1fr;
}
.price {
  position: relative;
  display: flex;
  flex-direction: column;
  gap: 14px;
  padding: 28px 24px;
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  background: var(--surface);
  transition: transform .3s var(--ease), border-color .3s var(--ease);
}
.price:hover { transform: translateY(-4px); }
.price--featured {
  border-color: rgba(124, 108, 255, .45);
  background:
    radial-gradient(90% 90% at 50% 0%, rgba(124, 108, 255, .16), transparent 65%),
    var(--surface-2);
  box-shadow: var(--glow);
}
.price__ribbon {
  position: absolute;
  top: -12px;
  left: 24px;
  padding: 3px 12px;
  border-radius: 999px;
  background: var(--grad);
  color: #0b0c14;
  font-size: .72rem;
  font-weight: 700;
  letter-spacing: .04em;
}
.price__name { font-size: 1.05rem; }
.price__amount {
  font-size: 2.2rem;
  font-weight: 700;
  letter-spacing: -.03em;
  line-height: 1.1;
}
.price__cur { font-size: 1.1rem; vertical-align: super; color: var(--text-muted); }
.price__desc { color: var(--text-muted); font-size: .88rem; }
.price .tick-list { flex: 1; margin-block: 4px 6px; }

/* 4.10 表单 */
.form {
  display: grid;
  gap: 20px;
  padding: 28px 22px;
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  background: var(--surface);
}
.form__row {
  display: grid;
  gap: 20px;
  grid-template-columns: 1fr;
}
.field { display: grid; gap: 8px; }
.field__label {
  color: var(--text-muted);
  font-size: .88rem;
  font-weight: 600;
}
.req { color: var(--danger); }

.field__input {
  width: 100%;
  padding: 12px 14px;
  border: 1px solid var(--border-strong);
  border-radius: var(--radius-sm);
  background: var(--bg-alt);
  color: var(--text);
  font-size: .95rem;
  transition: border-color .2s var(--ease), box-shadow .2s var(--ease);
}
.field__input::placeholder { color: var(--text-dim); }
.field__input:focus {
  outline: none;
  border-color: var(--primary);
  box-shadow: 0 0 0 3px var(--primary-soft);
}
.field__input--area { resize: vertical; min-height: 100px; }

select.field__input {
  appearance: none;
  background-image: linear-gradient(45deg, transparent 50%, var(--text-dim) 50%),
                    linear-gradient(135deg, var(--text-dim) 50%, transparent 50%);
  background-position: calc(100% - 19px) 50%, calc(100% - 14px) 50%;
  background-size: 5px 5px, 5px 5px;
  background-repeat: no-repeat;
  padding-right: 38px;
}

.field--check {
  grid-template-columns: auto 1fr;
  align-items: start;
  gap: 10px;
  padding: 2px;
}
.field__check {
  width: 18px;
  height: 18px;
  margin-top: 3px;
  accent-color: var(--primary);
}
.field__check-label {
  color: var(--text-muted);
  font-size: .86rem;
  font-weight: 400;
}
.field__check-label a { color: var(--secondary); text-decoration: underline; }

.field__error {
  color: var(--danger);
  font-size: .8rem;
}

/* 校验失败态 */
.field__input[aria-invalid="true"] {
  border-color: var(--danger);
  box-shadow: 0 0 0 3px rgba(248, 113, 113, .14);
}

.form__status {
  min-height: 1.4em;
  font-size: .9rem;
  text-align: center;
}
.form__status.is-ok { color: var(--ok); }
.form__status.is-err { color: var(--danger); }

/* 4.11 页脚 */
.site-footer {
  margin-top: 20px;
  padding-top: 48px;
  border-top: 1px solid var(--border);
  background: var(--bg-alt);
}
.footer__inner {
  display: grid;
  gap: 32px;
  padding-bottom: 36px;
}
.footer__desc {
  margin-top: 10px;
  max-width: 30em;
  color: var(--text-dim);
  font-size: .88rem;
}
.footer__nav {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 24px;
}
.footer__title {
  margin-bottom: 12px;
  font-size: .82rem;
  letter-spacing: .1em;
  text-transform: uppercase;
  color: var(--text-dim);
}
.footer__col ul { display: grid; gap: 9px; }
.footer__col a {
  color: var(--text-muted);
  font-size: .9rem;
  transition: color .2s var(--ease);
}
.footer__col a:hover { color: var(--secondary); }

.footer__bottom {
  display: flex;
  flex-direction: column;
  gap: 8px;
  padding-block: 20px 28px;
  border-top: 1px solid var(--border);
  color: var(--text-dim);
  font-size: .82rem;
}

/* 4.12 返回顶部 */
.to-top {
  position: fixed;
  right: 18px;
  bottom: 18px;
  z-index: 90;
  display: grid;
  place-items: center;
  width: 44px;
  height: 44px;
  border: 1px solid var(--border-strong);
  border-radius: 50%;
  background: rgba(18, 20, 31, .9);
  color: var(--text);
  cursor: pointer;
  backdrop-filter: blur(8px);
  box-shadow: var(--shadow);
  transition: transform .25s var(--ease), border-color .25s var(--ease);
}
.to-top:hover {
  transform: translateY(-3px);
  border-color: var(--primary);
}

/* 4.13 滚动显现（仅在 JS 可用时生效，避免无 JS 时内容不可见） */
.js .reveal {
  opacity: 0;
  transform: translateY(20px);
  transition: opacity .6s var(--ease), transform .6s var(--ease);
}
.js .reveal.is-visible {
  opacity: 1;
  transform: none;
}

/* ---------- 5. 断点 ---------- */

/* ≥ 640px：两列起步 */
@media (min-width: 640px) {
  .section { padding-block: 80px; }

  .card-grid  { grid-template-columns: repeat(2, 1fr); }
  .quote-grid { grid-template-columns: repeat(2, 1fr); }
  .form__row  { grid-template-columns: repeat(2, 1fr); }
  .form       { padding: 34px 30px; }
  .stats      { grid-template-columns: repeat(4, 1fr); }
  .stat       { padding: 26px 18px; }
  .stat strong { font-size: 1.9rem; }
  .footer__bottom { flex-direction: row; justify-content: space-between; align-items: center; }
}

/* ≥ 900px：导航转为横向，三列网格 */
@media (min-width: 900px) {
  .nav-toggle { display: none; }

  .primary-nav {
    position: static;
    display: flex;
    flex-direction: row;
    align-items: center;
    gap: 8px;
    padding: 0;
    background: none;
    border: none;
    box-shadow: none;
  }
  .primary-nav__list { flex-direction: row; gap: 4px; }
  .primary-nav__list a {
    padding: 8px 12px;
    border-bottom: none;
    border-radius: 999px;
    font-size: .9rem;
  }
  .primary-nav__list a:hover,
  .primary-nav__list a.is-active {
    background: rgba(255, 255, 255, .06);
  }
  .primary-nav__cta { margin-top: 0; margin-left: 8px; }

  .card-grid  { grid-template-columns: repeat(3, 1fr); }
  .quote-grid { grid-template-columns: repeat(3, 1fr); }
  .price-grid { grid-template-columns: repeat(3, 1fr); align-items: start; }
  .price--featured { transform: scale(1.03); }
  .price--featured:hover { transform: scale(1.03) translateY(-4px); }

  .acc-item__head { padding: 22px 26px; }
  .acc-item__body { padding: 0 26px 24px; }

  .footer__inner { grid-template-columns: 1.4fr 1fr; }
  .footer__nav   { grid-template-columns: repeat(2, 1fr); }
}

/* ≥ 1024px：Hero 双栏 */
@media (min-width: 1024px) {
  .hero { padding-block: 72px 84px; }
  .hero__inner { grid-template-columns: 1.05fr .95fr; gap: 56px; }

  .instructor {
    grid-template-columns: auto 1fr;
    align-items: start;
    gap: 36px;
    padding: 44px 40px;
  }

  .to-top { right: 28px; bottom: 28px; }
}

/* ---------- 6. 偏好与打印 ---------- */

/* 尊重「减少动态效果」的系统设置 */
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *,
  *::before,
  *::after {
    animation-duration: .01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: .01ms !important;
  }
  .js .reveal { opacity: 1; transform: none; }
  .card:hover,
  .price:hover,
  .price--featured,
  .price--featured:hover { transform: none; }
}

/* 打印：去掉装饰，保留正文（方便导出 PDF 版课程介绍） */
@media print {
  .site-header,
  .to-top,
  .hero__glow,
  .countdown,
  .form { display: none !important; }
  body { background: #fff; color: #111; }
  .section, .card, .acc-item, .price, .quote, .instructor {
    border-color: #ddd !important;
    background: none !important;
    box-shadow: none !important;
    break-inside: avoid;
  }
  .grad-text { -webkit-text-fill-color: #111; color: #111; }
  .codewin { box-shadow: none; }
}