/* ============================================================
 * 首页：Hero、筛选、卡片网格、说明区
 * ============================================================ */

/* ---------------- Hero ---------------- */
.hero {
  position: relative;
  margin: 34px 0 30px;
  padding: 40px 44px 36px;
  border-radius: var(--r-xl);
  background:
    radial-gradient(1100px 380px at 12% -10%, rgba(79, 70, 229, .13), transparent 62%),
    radial-gradient(900px 340px at 92% 6%, rgba(8, 145, 178, .13), transparent 60%),
    var(--surface);
  border: 1px solid var(--line);
  box-shadow: var(--sh-2);
  overflow: hidden;
}

.hero::after {
  content: "";
  position: absolute;
  right: -80px;
  bottom: -120px;
  width: 340px;
  height: 340px;
  border-radius: 50%;
  background: var(--grad);
  opacity: .05;
  filter: blur(6px);
}

.hero-inner {
  position: relative;
  max-width: 880px;
}

.hero-title {
  margin: 0 0 14px;
  font-size: clamp(28px, 4.1vw, 46px);
  line-height: 1.2;
  letter-spacing: -.022em;
  font-weight: 720;
}

.hero-title em {
  font-style: normal;
  background: var(--grad);
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
  padding: 0 .06em;
}

.hero-sub {
  color: var(--muted);
  font-size: 16px;
  max-width: 720px;
}

.hero-search {
  position: relative;
  margin: 26px 0 0;
  max-width: 560px;
}

.search-input {
  width: 100%;
  padding: 13px 110px 13px 18px;
  border-radius: 14px;
  border: 1px solid var(--line-2);
  background: var(--surface);
  font-size: 14.5px;
  outline: none;
  transition: border .16s, box-shadow .16s;
}

.search-input:focus {
  border-color: rgba(79, 70, 229, .5);
  box-shadow: 0 0 0 4px rgba(79, 70, 229, .1);
}

.search-kbd {
  position: absolute;
  right: 14px;
  top: 50%;
  transform: translateY(-50%);
  font-size: 11.5px;
  color: var(--muted-2);
  background: var(--bg-soft);
  padding: 3px 9px;
  border-radius: 7px;
  pointer-events: none;
}

/* ---------------- 筛选条 ---------------- */
.filters {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  margin: 0 0 10px;
}

.filter-results {
  margin: 0 0 20px;
  color: var(--muted);
  font-size: 13px;
}

.filter-empty {
  margin: 20px 0 48px;
  padding: 36px 28px;
  border: 1px dashed var(--line-2);
  border-radius: var(--r-lg);
  background: var(--surface);
  text-align: center;
}

.filter-empty h2 { font-size: 18px; }
.filter-empty p { margin: 8px 0 18px; color: var(--muted); }

.chip {
  padding: 8px 16px;
  border-radius: 999px;
  border: 1px solid var(--line-2);
  background: var(--surface);
  color: var(--ink-2);
  font-size: 13.5px;
  font-weight: 500;
  cursor: pointer;
  transition: all .16s;
}

.chip:hover {
  border-color: #c7cede;
  transform: translateY(-1px);
}

.chip.is-on {
  background: var(--ink);
  border-color: var(--ink);
  color: #fff;
  box-shadow: 0 6px 16px -8px rgba(15, 23, 42, .6);
}

/* 动态缩略图开关：推到筛选栏右端，视觉上与分类 chip 区分 */
.filters .chip-anim {
  margin-left: auto;
  border-style: dashed;
  border-color: rgba(8, 145, 178, .4);
  color: var(--brand-2);
  font-variant-numeric: tabular-nums;
}

.filters .chip-anim:hover {
  border-color: var(--brand-2);
  background: var(--brand-soft-2);
}

.filters .chip-anim.is-on {
  border-style: solid;
  border-color: var(--brand-2);
  background: var(--brand-2);
  color: #fff;
  box-shadow: 0 6px 16px -8px rgba(8, 145, 178, .8);
}

/* ---------------- 分类与卡片 ---------------- */
.cat-section {
  margin-bottom: 42px;
}

.cat-head {
  display: flex;
  align-items: baseline;
  gap: 14px;
  margin-bottom: 16px;
  padding-bottom: 12px;
  border-bottom: 1px solid var(--line);
}

.cat-title {
  font-size: 18.5px;
  letter-spacing: -.01em;
}

.cat-title::before {
  content: "";
  display: inline-block;
  width: 4px;
  height: 16px;
  border-radius: 3px;
  background: var(--grad);
  margin-right: 10px;
  vertical-align: -2px;
}

.cat-desc {
  color: var(--muted-2);
  font-size: 13px;
}

.grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(268px, 1fr));
  gap: 20px;
}

.card {
  position: relative;
  display: flex;
  flex-direction: column;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--r-lg);
  overflow: hidden;
  color: inherit;
  box-shadow: var(--sh-1);
  transition: transform .2s cubic-bezier(.2, .7, .3, 1), box-shadow .2s, border-color .2s;
}

.card:hover {
  transform: translateY(-4px);
  box-shadow: var(--sh-3);
  border-color: #d3d9e6;
}

.card-thumb {
  position: relative;
  height: 168px;
  background: linear-gradient(160deg, #f7f9fd, #eef2f9);
  border-bottom: 1px solid var(--line);
}

.card-thumb[data-cat="oscillation"] {
  background: linear-gradient(160deg, #f4f4ff, #eaeafb);
}

.card-thumb[data-cat="coupling"] {
  background: linear-gradient(160deg, #f2f8fb, #e6f1f7);
}

.card-thumb[data-cat="collision"] {
  background: linear-gradient(160deg, #fdf4f5, #fbe9ec);
}

.card-thumb[data-cat="mechanics"] {
  background: linear-gradient(160deg, #f4f9f5, #e8f2ea);
}

.card-thumb[data-cat="wave"] {
  background: linear-gradient(160deg, #f6f4fd, #ece7fa);
}

.thumb-canvas {
  display: block;
  width: 100%;
  height: 100%;
}

.card-body {
  padding: 15px 17px 18px;
  flex: 1;
}

.card-title {
  font-size: 16px;
  letter-spacing: -.01em;
}

.card-sum {
  margin-top: 7px;
  color: var(--muted);
  font-size: 13px;
  line-height: 1.62;
  display: -webkit-box;
  -webkit-line-clamp: 3;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

.card-tags {
  display: flex;
  gap: 6px;
  flex-wrap: wrap;
  margin-top: 13px;
}

.card-go {
  position: absolute;
  top: 14px;
  right: 14px;
  padding: 4px 11px;
  border-radius: 999px;
  background: rgba(255, 255, 255, .88);
  backdrop-filter: blur(6px);
  border: 1px solid var(--line-2);
  font-size: 11.5px;
  color: var(--ink-2);
  font-weight: 600;
  opacity: 0;
  transform: translateY(-4px);
  transition: all .2s;
}

.card:hover .card-go {
  opacity: 1;
  transform: translateY(0);
}

.card:focus-visible .card-go {
  opacity: 1;
  transform: translateY(0);
}

@media (hover: none) {
  .card-go {
    opacity: 1;
    transform: none;
  }
}

/* ---------------- 说明区 ---------------- */
.notes {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 20px;
  margin-top: 12px;
}

.note {
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--r-lg);
  padding: 22px 24px;
  box-shadow: var(--sh-1);
}

.note-title {
  font-size: 15px;
  margin-bottom: 12px;
  display: flex;
  align-items: center;
  gap: 9px;
}

.note-title::before {
  content: "";
  width: 7px;
  height: 7px;
  border-radius: 50%;
  background: var(--grad);
}

.note-list li {
  position: relative;
  padding-left: 18px;
  margin-bottom: 9px;
  color: var(--muted);
  font-size: 13.5px;
  line-height: 1.65;
}

.note-list li::before {
  content: "";
  position: absolute;
  left: 3px;
  top: 9px;
  width: 5px;
  height: 5px;
  border-radius: 50%;
  background: var(--line-2);
}

.note-list li:last-child {
  margin-bottom: 0;
}

@media (min-width: 721px) and (max-width: 1100px) {
  .filters { gap: 6px; }
  .filters .chip { padding: 8px 11px; font-size: 12.5px; }
}

@media (max-width: 720px) {
  .hero {
    padding: 28px 22px 24px;
    margin-top: 20px;
    border-radius: var(--r-lg);
  }

  .grid {
    grid-template-columns: repeat(auto-fill, minmax(230px, 1fr));
    gap: 14px;
  }

  .card-thumb {
    height: 140px;
  }

  .cat-head {
    flex-direction: column;
    gap: 4px;
  }
}