/* ===== 基础重置 ===== */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

:root {
  --brand: #4f46e5;
  --brand-dark: #4338ca;
  --bg: #f7f8fc;
  --card-bg: #ffffff;
  --text: #1f2937;
  --text-soft: #6b7280;
  --border: #e5e7eb;
  --radius: 14px;
  --shadow: 0 6px 20px rgba(31, 41, 55, 0.08);
  --shadow-hover: 0 14px 34px rgba(79, 70, 229, 0.18);
  --maxw: 1180px;
}

html {
  scroll-behavior: smooth;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC",
    "Microsoft YaHei", "Helvetica Neue", Arial, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
}

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

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

/* ===== 顶部导航（所有页面同步） ===== */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(255, 255, 255, 0.9);
  backdrop-filter: saturate(180%) blur(10px);
  border-bottom: 1px solid var(--border);
}

.nav {
  max-width: var(--maxw);
  margin: 0 auto;
  height: 64px;
  padding: 0 20px;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.nav .logo {
  font-size: 20px;
  font-weight: 800;
  color: var(--brand);
  letter-spacing: 0.5px;
}

.nav .logo span {
  color: var(--text);
}

.nav ul {
  list-style: none;
  display: flex;
  gap: 28px;
}

.nav ul a {
  font-size: 15px;
  font-weight: 500;
  color: var(--text-soft);
  padding: 6px 0;
  position: relative;
  transition: color 0.2s;
}

.nav ul a:hover,
.nav ul a.active {
  color: var(--brand);
}

.nav ul a.active::after {
  content: "";
  position: absolute;
  left: 0;
  right: 0;
  bottom: -2px;
  height: 3px;
  border-radius: 3px;
  background: var(--brand);
}

/* ===== 通用容器 ===== */
.container {
  max-width: var(--maxw);
  margin: 0 auto;
  padding: 0 20px;
}

/* ===== 首页：工具卡片网格 ===== */
.tools-section {
  padding: 30px 0 70px;
}

.section-title {
  font-size: 24px;
  margin-bottom: 24px;
  text-align: center;
}

/* 首页分段大标题 */
.subsection {
  margin-bottom: 52px;
}

.subsection:last-child {
  margin-bottom: 0;
}

.cat-title {
  font-size: 27px;
  font-weight: 800;
  margin-bottom: 22px;
  padding-left: 14px;
  border-left: 5px solid var(--brand);
  color: var(--text);
}

@media (max-width: 600px) {
  .cat-title {
    font-size: 22px;
  }
}

/* 展示更多按钮（每段超过 3 个时自动出现） */
.show-more {
  display: block;
  margin: 20px auto 0;
  padding: 10px 30px;
  font-size: 14px;
  font-weight: 600;
  color: var(--brand);
  background: #fff;
  border: 1px solid var(--brand);
  border-radius: 999px;
  cursor: pointer;
  transition: background 0.2s, color 0.2s;
}

.show-more:hover {
  background: var(--brand);
  color: #fff;
}

.card.is-hidden {
  display: none;
}

/* ===== 夜间模式开关 ===== */
#theme-toggle {
  width: 36px;
  height: 36px;
  border-radius: 50%;
  border: 1px solid var(--border);
  background: transparent;
  color: var(--text);
  cursor: pointer;
  font-size: 16px;
  line-height: 1;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  transition: background 0.2s, transform 0.2s;
}

#theme-toggle:hover {
  background: rgba(127, 127, 127, 0.15);
  transform: scale(1.06);
}

/* ===== 回到顶部按钮 ===== */
#back-top {
  position: fixed;
  right: 24px;
  bottom: 24px;
  width: 44px;
  height: 44px;
  border: none;
  border-radius: 50%;
  background: var(--brand);
  color: #fff;
  font-size: 20px;
  cursor: pointer;
  box-shadow: var(--shadow);
  opacity: 0;
  visibility: hidden;
  transform: translateY(10px);
  transition: opacity 0.25s, transform 0.25s, visibility 0.25s, background 0.2s;
  z-index: 200;
}

#back-top.show {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}

#back-top:hover {
  background: var(--brand-dark);
}

/* ===== 夜间模式主题变量 ===== */
html.dark {
  --bg: #0f1115;
  --card-bg: #1a1d24;
  --text: #e5e7eb;
  --text-soft: #9aa3b2;
  --border: #2a2f3a;
  --shadow: 0 6px 20px rgba(0, 0, 0, 0.45);
  --shadow-hover: 0 14px 34px rgba(0, 0, 0, 0.6);
}

html.dark .site-header {
  background: rgba(15, 17, 21, 0.9);
  border-bottom-color: var(--border);
}

html.dark .site-footer {
  background: #15181e;
  border-top-color: var(--border);
}

html.dark .card {
  border-color: var(--border);
}

.grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 26px;
}

.card {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
  box-shadow: var(--shadow);
  transition: transform 0.22s ease, box-shadow 0.22s ease;
  display: flex;
  flex-direction: column;
}

.card:hover {
  transform: translateY(-6px);
  box-shadow: var(--shadow-hover);
}

.card .thumb {
  aspect-ratio: 16 / 10;
  width: 100%;
  object-fit: cover;
  background: #eef0f6;
}

.card .body {
  padding: 18px 18px 22px;
  flex: 1;
  display: flex;
  flex-direction: column;
}

.card .body h3 {
  font-size: 18px;
  margin-bottom: 8px;
}

.card .body p {
  font-size: 14px;
  color: var(--text-soft);
  flex: 1;
}

.card .more {
  margin-top: 14px;
  align-self: flex-start;
  font-size: 14px;
  font-weight: 600;
  color: var(--brand);
  display: inline-flex;
  align-items: center;
  gap: 4px;
}

.card .more::after {
  content: "→";
  transition: transform 0.2s;
}

.card:hover .more::after {
  transform: translateX(4px);
}

/* ===== 二级页：文章 ===== */
.article {
  padding: 40px 0 70px;
}

.breadcrumb {
  font-size: 13px;
  color: var(--text-soft);
  margin-bottom: 18px;
}

.breadcrumb a:hover {
  color: var(--brand);
}

.article-head {
  display: flex;
  gap: 28px;
  align-items: flex-start;
  flex-wrap: wrap;
}

.article-head .cover {
  width: 360px;
  max-width: 100%;
  border-radius: var(--radius);
  border: 1px solid var(--border);
  box-shadow: var(--shadow);
}

.article-head .meta {
  flex: 1;
  min-width: 260px;
}

.article-head h1 {
  font-size: 30px;
  margin-bottom: 12px;
}

.article-head .tag {
  display: inline-block;
  font-size: 13px;
  font-weight: 600;
  color: var(--brand);
  background: rgba(79, 70, 229, 0.1);
  padding: 4px 12px;
  border-radius: 999px;
  margin-bottom: 14px;
}

.article-head .lead {
  color: var(--text-soft);
  font-size: 16px;
}

.article-body {
  margin-top: 36px;
}

.article-body h2 {
  font-size: 21px;
  margin: 28px 0 12px;
  padding-left: 12px;
  border-left: 4px solid var(--brand);
}

.article-body p,
.article-body li {
  font-size: 15.5px;
  color: #374151;
  margin-bottom: 10px;
}

.article-body ul {
  padding-left: 22px;
}

.btn-download {
  display: inline-block;
  margin-top: 18px;
  background: var(--brand);
  color: #fff;
  font-weight: 600;
  padding: 12px 26px;
  border-radius: 10px;
  transition: background 0.2s, transform 0.2s;
}

.btn-download:hover {
  background: var(--brand-dark);
  transform: translateY(-2px);
}

/* ===== 页脚 ===== */
.site-footer {
  border-top: 1px solid var(--border);
  background: #fff;
  padding: 26px 0;
  text-align: center;
  color: var(--text-soft);
  font-size: 14px;
}

/* ===== 响应式 ===== */
@media (max-width: 900px) {
  .grid {
    grid-template-columns: repeat(2, 1fr);
  }
}

@media (max-width: 600px) {
  .hero h1 {
    font-size: 30px;
  }
  .grid {
    grid-template-columns: 1fr;
  }
  .nav ul {
    gap: 16px;
  }
  .nav .logo {
    font-size: 17px;
  }
}