/* ============================================
   铁旗传媒官网 - 全局样式表
   版本：2026 v2.0
   设计：深色科技感 + 铁旗红
   ============================================ */

/* ===== 设计令牌 ===== */
:root {
  /* 品牌色 */
  --brand: #C7000A;
  --brand-light: #E5132A;
  --brand-dark: #9E0008;
  --brand-glow: rgba(199, 0, 10, 0.35);

  /* 背景色 */
  --bg: #0A0A0C;
  --bg-alt: #121216;
  --bg-card: #17171C;
  --bg-card-hover: #1E1E25;

  /* 文字色 */
  --text: #FFFFFF;
  --text-soft: #C9C9D1;
  --text-muted: #8B8B96;

  /* 描边 */
  --border: rgba(255, 255, 255, 0.08);
  --border-strong: rgba(255, 255, 255, 0.14);

  /* 间距 */
  --section-pad: 96px;
  --radius: 16px;
  --radius-sm: 10px;

  /* 容器 */
  --max-width: 1200px;

  /* 动效 */
  --ease: cubic-bezier(0.4, 0, 0.2, 1);
  --transition: 0.3s var(--ease);
}

/* ===== Reset ===== */
*,
*::before,
*::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

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

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC",
    "Hiragino Sans GB", "Microsoft YaHei", "Helvetica Neue", sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.7;
  font-size: 16px;
  overflow-x: hidden;
  -webkit-font-smoothing: antialiased;
}

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

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

ul {
  list-style: none;
}

button {
  font-family: inherit;
  cursor: pointer;
  border: none;
  background: none;
  color: inherit;
}

/* ===== 布局容器 ===== */
.container {
  width: 100%;
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 24px;
}

.section {
  padding: var(--section-pad) 0;
}

.section-sm {
  padding: 64px 0;
}

/* ===== 导航栏 ===== */
.navbar {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 1000;
  background: rgba(10, 10, 12, 0.72);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border-bottom: 1px solid transparent;
  transition: var(--transition);
}

.navbar.scrolled {
  background: rgba(10, 10, 12, 0.94);
  border-bottom-color: var(--border);
}

.navbar .container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 72px;
}

.nav-logo {
  font-weight: 800;
  font-size: 1.5rem;
  letter-spacing: -0.02em;
  display: flex;
  align-items: center;
  gap: 8px;
}

.logo-mark {
  color: var(--brand);
}

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

.nav-links {
  display: flex;
  align-items: center;
  gap: 32px;
}

.nav-links a {
  font-size: 0.95rem;
  color: var(--text-soft);
  transition: color var(--transition);
  position: relative;
}

.nav-links a:hover {
  color: var(--text);
}

.nav-links a.active {
  color: var(--text);
}

.nav-links a.active::after {
  content: "";
  position: absolute;
  bottom: -6px;
  left: 0;
  width: 20px;
  height: 2px;
  background: var(--brand);
  border-radius: 2px;
}

.nav-cta {
  background: var(--brand);
  color: var(--text) !important;
  padding: 9px 20px;
  border-radius: 8px;
  font-weight: 500;
  transition: background var(--transition);
}

.nav-cta:hover {
  background: var(--brand-light);
}

/* 移动端菜单按钮 */
.menu-toggle {
  display: none;
  flex-direction: column;
  gap: 5px;
  padding: 8px;
}

.menu-toggle span {
  display: block;
  width: 22px;
  height: 2px;
  background: var(--text);
  border-radius: 2px;
  transition: var(--transition);
}

/* ===== 按钮 ===== */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 14px 28px;
  border-radius: 10px;
  font-size: 1rem;
  font-weight: 500;
  transition: var(--transition);
  border: 1px solid transparent;
}

.btn-primary {
  background: var(--brand);
  color: var(--text);
  box-shadow: 0 4px 20px var(--brand-glow);
}

.btn-primary:hover {
  background: var(--brand-light);
  transform: translateY(-2px);
  box-shadow: 0 8px 28px var(--brand-glow);
}

.btn-outline {
  border-color: var(--border-strong);
  color: var(--text-soft);
}

.btn-outline:hover {
  border-color: var(--brand);
  color: var(--text);
  background: rgba(199, 0, 10, 0.08);
}

.btn-lg {
  padding: 16px 36px;
  font-size: 1.05rem;
}

/* ===== Hero 区域 ===== */
.hero {
  position: relative;
  padding: 160px 0 80px;
  overflow: hidden;
}

.hero-bg {
  position: absolute;
  top: -20%;
  left: 50%;
  transform: translateX(-50%);
  width: 900px;
  height: 900px;
  background: radial-gradient(
    circle,
    rgba(199, 0, 10, 0.16) 0%,
    rgba(199, 0, 10, 0.05) 40%,
    transparent 70%
  );
  pointer-events: none;
}

.hero-grid {
  position: absolute;
  inset: 0;
  background-image: linear-gradient(var(--border) 1px, transparent 1px),
    linear-gradient(90deg, var(--border) 1px, transparent 1px);
  background-size: 64px 64px;
  mask-image: radial-gradient(ellipse 80% 60% at 50% 40%, #000 20%, transparent 75%);
  -webkit-mask-image: radial-gradient(
    ellipse 80% 60% at 50% 40%,
    #000 20%,
    transparent 75%
  );
  opacity: 0.5;
  pointer-events: none;
}

.hero-content {
  position: relative;
  text-align: center;
  max-width: 820px;
  margin: 0 auto;
}

.hero-badge {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 7px 16px;
  border-radius: 999px;
  border: 1px solid var(--border-strong);
  background: var(--bg-card);
  font-size: 0.875rem;
  color: var(--text-soft);
  margin-bottom: 28px;
}

.hero-title {
  font-size: clamp(2.25rem, 5.5vw, 4rem);
  font-weight: 800;
  line-height: 1.2;
  letter-spacing: -0.03em;
  margin-bottom: 24px;
}

.hero-title .highlight {
  color: var(--brand);
}

.hero-desc {
  font-size: 1.125rem;
  color: var(--text-muted);
  max-width: 640px;
  margin: 0 auto 40px;
}

.hero-actions {
  display: flex;
  gap: 16px;
  justify-content: center;
  flex-wrap: wrap;
  margin-bottom: 72px;
}

/* 数据统计卡片 */
.hero-stats {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 20px;
}

.stat-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 28px 20px;
  text-align: center;
  transition: var(--transition);
}

.stat-card:hover {
  background: var(--bg-card-hover);
  border-color: var(--border-strong);
  transform: translateY(-4px);
}

.stat-number {
  font-size: 2rem;
  font-weight: 800;
  color: var(--brand);
  line-height: 1.2;
  letter-spacing: -0.02em;
}

.stat-label {
  font-size: 0.875rem;
  color: var(--text-muted);
  margin-top: 6px;
}

/* ===== 区块头部 ===== */
.section-header {
  text-align: center;
  margin-bottom: 56px;
}

.section-tag {
  display: inline-block;
  font-size: 0.8125rem;
  font-weight: 600;
  letter-spacing: 0.12em;
  color: var(--brand);
  text-transform: uppercase;
  margin-bottom: 12px;
}

.section-title {
  font-size: clamp(1.75rem, 3.5vw, 2.5rem);
  font-weight: 700;
  letter-spacing: -0.02em;
  margin-bottom: 14px;
}

.section-desc {
  color: var(--text-muted);
  font-size: 1.0625rem;
  max-width: 620px;
  margin: 0 auto;
}

/* ===== 服务卡片 ===== */
.services-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 24px;
}

.service-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 36px 28px;
  transition: var(--transition);
}

.service-card:hover {
  background: var(--bg-card-hover);
  border-color: var(--border-strong);
  transform: translateY(-6px);
}

.service-icon {
  width: 52px;
  height: 52px;
  border-radius: 12px;
  background: rgba(199, 0, 10, 0.12);
  border: 1px solid rgba(199, 0, 10, 0.25);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.5rem;
  margin-bottom: 20px;
}

.service-card h3 {
  font-size: 1.25rem;
  font-weight: 600;
  margin-bottom: 12px;
}

.service-card p {
  color: var(--text-muted);
  font-size: 0.9375rem;
}

/* ===== 区域覆盖 ===== */
.region-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 24px;
}

.region-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 32px;
  transition: var(--transition);
}

.region-card:hover {
  border-color: var(--border-strong);
  background: var(--bg-card-hover);
}

.region-card h3 {
  font-size: 1.375rem;
  margin-bottom: 8px;
  display: flex;
  align-items: center;
  gap: 10px;
}

.region-count {
  font-size: 0.875rem;
  color: var(--brand);
  font-weight: 600;
  background: rgba(199, 0, 10, 0.1);
  padding: 3px 10px;
  border-radius: 6px;
}

.region-card p {
  color: var(--text-muted);
  font-size: 0.9375rem;
  margin-bottom: 18px;
}

.region-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}

.tag {
  font-size: 0.8125rem;
  color: var(--text-soft);
  background: var(--bg-alt);
  border: 1px solid var(--border);
  padding: 4px 11px;
  border-radius: 6px;
}

/* ===== 客户品牌墙 ===== */
.clients-grid {
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  gap: 16px;
}

.client-item {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 26px 16px;
  text-align: center;
  transition: var(--transition);
}

.client-item:hover {
  border-color: var(--border-strong);
  background: var(--bg-card-hover);
  transform: translateY(-3px);
}

.client-name {
  font-weight: 600;
  font-size: 1.0625rem;
  margin-bottom: 4px;
}

.client-industry {
  font-size: 0.8125rem;
  color: var(--text-muted);
}

/* ===== 服务流程 ===== */
.process-grid {
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  gap: 20px;
  counter-reset: step;
}

.process-step {
  position: relative;
  text-align: center;
  padding: 32px 16px;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  transition: var(--transition);
}

.process-step:hover {
  background: var(--bg-card-hover);
  transform: translateY(-4px);
}

.process-num {
  width: 40px;
  height: 40px;
  margin: 0 auto 16px;
  border-radius: 50%;
  background: var(--brand);
  color: var(--text);
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: 1.0625rem;
}

.process-step h4 {
  font-size: 1.0625rem;
  margin-bottom: 8px;
}

.process-step p {
  font-size: 0.875rem;
  color: var(--text-muted);
}

/* ===== FAQ ===== */
.faq-list {
  max-width: 820px;
  margin: 0 auto;
}

.faq-item {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  margin-bottom: 12px;
  overflow: hidden;
  transition: var(--transition);
}

.faq-item:hover {
  border-color: var(--border-strong);
}

.faq-question {
  width: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  padding: 20px 24px;
  text-align: left;
  font-size: 1.0625rem;
  font-weight: 500;
  color: var(--text);
}

.faq-question .arrow {
  flex-shrink: 0;
  color: var(--brand);
  font-size: 0.875rem;
  transition: transform var(--transition);
}

.faq-item.open .faq-question .arrow {
  transform: rotate(90deg);
}

.faq-answer {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.35s var(--ease);
}

.faq-item.open .faq-answer {
  max-height: 600px;
}

.faq-answer-inner {
  padding: 0 24px 22px;
  color: var(--text-muted);
  font-size: 0.9375rem;
}

/* FAQ 预览（首页） */
.faq-preview-list {
  max-width: 820px;
  margin: 0 auto;
}

.faq-preview-item {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  padding: 18px 24px;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  margin-bottom: 10px;
  transition: var(--transition);
}

.faq-preview-item:hover {
  border-color: var(--brand);
  background: var(--bg-card-hover);
}

.faq-preview-item .q {
  font-size: 1rem;
  font-weight: 500;
}

.faq-preview-item .arrow {
  color: var(--brand);
}

.faq-cta {
  text-align: center;
  margin-top: 28px;
}

/* ===== CTA 区块 ===== */
.cta-box {
  background: linear-gradient(135deg, rgba(199, 0, 10, 0.12), rgba(199, 0, 10, 0.02));
  border: 1px solid rgba(199, 0, 10, 0.25);
  border-radius: 24px;
  padding: 64px 32px;
  text-align: center;
}

.cta-box h2 {
  font-size: clamp(1.5rem, 3vw, 2.25rem);
  font-weight: 700;
  margin-bottom: 14px;
}

.cta-box p {
  color: var(--text-muted);
  font-size: 1.0625rem;
  margin-bottom: 32px;
}

.cta-actions {
  display: flex;
  gap: 14px;
  justify-content: center;
  flex-wrap: wrap;
}

/* ===== 媒体资源页 ===== */
.filter-bar {
  display: flex;
  gap: 12px;
  justify-content: center;
  flex-wrap: wrap;
  margin-bottom: 40px;
}

.filter-btn {
  padding: 9px 22px;
  border-radius: 999px;
  border: 1px solid var(--border-strong);
  font-size: 0.9375rem;
  color: var(--text-soft);
  transition: var(--transition);
}

.filter-btn:hover {
  border-color: var(--brand);
  color: var(--text);
}

.filter-btn.active {
  background: var(--brand);
  border-color: var(--brand);
  color: var(--text);
}

.projects-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 20px;
}

.project-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 26px 24px;
  transition: var(--transition);
}

.project-card:hover {
  background: var(--bg-card-hover);
  border-color: var(--brand);
  transform: translateY(-4px);
}

.project-district {
  display: inline-block;
  font-size: 0.75rem;
  font-weight: 600;
  color: var(--brand);
  background: rgba(199, 0, 10, 0.1);
  padding: 3px 9px;
  border-radius: 5px;
  margin-bottom: 12px;
}

.project-card h3 {
  font-size: 1.125rem;
  font-weight: 600;
  margin-bottom: 8px;
}

.project-card p {
  font-size: 0.875rem;
  color: var(--text-muted);
}

.project-type {
  display: inline-block;
  margin-top: 12px;
  font-size: 0.75rem;
  color: var(--text-muted);
  border: 1px solid var(--border);
  padding: 2px 8px;
  border-radius: 5px;
}

/* ===== 案例页 ===== */
.cases-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 24px;
}

.case-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
  transition: var(--transition);
}

.case-card:hover {
  border-color: var(--brand);
  transform: translateY(-6px);
}

.case-visual {
  height: 120px;
  background: linear-gradient(135deg, rgba(199, 0, 10, 0.18), rgba(199, 0, 10, 0.04));
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 2rem;
  border-bottom: 1px solid var(--border);
}

.case-body {
  padding: 24px;
}

.case-industry {
  font-size: 0.75rem;
  color: var(--brand);
  font-weight: 600;
  margin-bottom: 8px;
}

.case-card h3 {
  font-size: 1.125rem;
  font-weight: 600;
  margin-bottom: 10px;
}

.case-card p {
  font-size: 0.9375rem;
  color: var(--text-muted);
  margin-bottom: 16px;
}

.case-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
}

.case-tags span {
  font-size: 0.75rem;
  color: var(--text-soft);
  background: var(--bg-alt);
  border: 1px solid var(--border);
  padding: 3px 9px;
  border-radius: 5px;
}

/* ===== 关于页 ===== */
.about-intro {
  display: grid;
  grid-template-columns: 1.2fr 1fr;
  gap: 48px;
  align-items: center;
}

.about-text p {
  color: var(--text-muted);
  margin-bottom: 16px;
  font-size: 1rem;
}

.info-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 28px;
}

.info-card h4 {
  font-size: 1rem;
  margin-bottom: 18px;
  color: var(--text);
}

.info-list li {
  display: flex;
  justify-content: space-between;
  gap: 16px;
  padding: 10px 0;
  border-bottom: 1px solid var(--border);
  font-size: 0.9375rem;
}

.info-list li:last-child {
  border-bottom: none;
}

.info-list .label {
  color: var(--text-muted);
  flex-shrink: 0;
}

.info-list .value {
  color: var(--text-soft);
  text-align: right;
}

/* 发展历程 */
.timeline {
  max-width: 780px;
  margin: 0 auto;
  position: relative;
  padding-left: 32px;
}

.timeline::before {
  content: "";
  position: absolute;
  left: 7px;
  top: 8px;
  bottom: 8px;
  width: 2px;
  background: linear-gradient(180deg, var(--brand), rgba(199, 0, 10, 0.1));
}

.timeline-item {
  position: relative;
  padding-bottom: 36px;
}

.timeline-item::before {
  content: "";
  position: absolute;
  left: -32px;
  top: 6px;
  width: 16px;
  height: 16px;
  border-radius: 50%;
  background: var(--brand);
  border: 3px solid var(--bg);
}

.timeline-date {
  font-size: 0.8125rem;
  color: var(--brand);
  font-weight: 600;
  margin-bottom: 6px;
}

.timeline-item h4 {
  font-size: 1.125rem;
  margin-bottom: 8px;
}

.timeline-item p {
  color: var(--text-muted);
  font-size: 0.9375rem;
}

/* 优势卡片 */
.advantages-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 20px;
}

.advantage-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 30px 24px;
  transition: var(--transition);
}

.advantage-card:hover {
  border-color: var(--brand);
  background: var(--bg-card-hover);
  transform: translateY(-4px);
}

.advantage-icon {
  font-size: 1.75rem;
  margin-bottom: 14px;
}

.advantage-card h4 {
  font-size: 1.0625rem;
  margin-bottom: 8px;
}

.advantage-card p {
  font-size: 0.875rem;
  color: var(--text-muted);
}

/* ===== 联系页 ===== */
.contact-grid {
  display: grid;
  grid-template-columns: 1fr 1.1fr;
  gap: 40px;
  align-items: start;
}

.contact-info-list {
  display: flex;
  flex-direction: column;
  gap: 16px;
}

.contact-item {
  display: flex;
  gap: 16px;
  padding: 22px;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  transition: var(--transition);
}

.contact-item:hover {
  border-color: var(--brand);
  background: var(--bg-card-hover);
}

.contact-icon {
  font-size: 1.375rem;
  flex-shrink: 0;
}

.contact-item .label {
  font-size: 0.8125rem;
  color: var(--text-muted);
  margin-bottom: 3px;
}

.contact-item .value {
  font-size: 1rem;
  color: var(--text);
  font-weight: 500;
}

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

/* 表单 */
.form-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 36px;
}

.form-card h3 {
  font-size: 1.375rem;
  margin-bottom: 6px;
}

.form-sub {
  color: var(--text-muted);
  font-size: 0.9375rem;
  margin-bottom: 26px;
}

.form-row {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 16px;
  margin-bottom: 16px;
}

.form-group {
  margin-bottom: 16px;
}

.form-group label {
  display: block;
  font-size: 0.875rem;
  color: var(--text-soft);
  margin-bottom: 7px;
}

.form-group label .req {
  color: var(--brand);
}

.form-group input,
.form-group textarea {
  width: 100%;
  padding: 12px 14px;
  background: var(--bg-alt);
  border: 1px solid var(--border);
  border-radius: 8px;
  color: var(--text);
  font-size: 0.9375rem;
  font-family: inherit;
  transition: var(--transition);
}

.form-group input:focus,
.form-group textarea:focus {
  outline: none;
  border-color: var(--brand);
  background: var(--bg-card-hover);
}

.form-group textarea {
  resize: vertical;
  min-height: 110px;
}

.form-note {
  font-size: 0.8125rem;
  color: var(--text-muted);
  margin-top: 14px;
  text-align: center;
}

.form-success {
  display: none;
  padding: 16px;
  background: rgba(34, 197, 94, 0.1);
  border: 1px solid rgba(34, 197, 94, 0.3);
  border-radius: 8px;
  color: #4ADE80;
  font-size: 0.9375rem;
  text-align: center;
  margin-top: 16px;
}

.form-success.show {
  display: block;
}

/* ===== 页脚 ===== */
.footer {
  background: var(--bg-alt);
  border-top: 1px solid var(--border);
  padding: 64px 0 28px;
  margin-top: 40px;
}

.footer-grid {
  display: grid;
  grid-template-columns: 2fr 1fr 1fr 1.2fr;
  gap: 40px;
  margin-bottom: 44px;
}

.footer-brand p {
  color: var(--text-muted);
  font-size: 0.875rem;
  margin: 16px 0;
  max-width: 340px;
}

.footer-social {
  display: flex;
  gap: 10px;
}

.footer-social a {
  width: 38px;
  height: 38px;
  border-radius: 8px;
  background: var(--bg-card);
  border: 1px solid var(--border);
  display: flex;
  align-items: center;
  justify-content: center;
  transition: var(--transition);
}

.footer-social a:hover {
  border-color: var(--brand);
  background: var(--bg-card-hover);
}

.footer h4 {
  font-size: 0.9375rem;
  font-weight: 600;
  margin-bottom: 16px;
}

.footer-links li {
  margin-bottom: 10px;
}

.footer-links a,
.footer-links li {
  font-size: 0.875rem;
  color: var(--text-muted);
  transition: color var(--transition);
}

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

.footer-bottom {
  border-top: 1px solid var(--border);
  padding-top: 24px;
  text-align: center;
  font-size: 0.8125rem;
  color: var(--text-muted);
}

.footer-bottom p {
  margin-bottom: 8px;
}

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

/* ===== 返回顶部 ===== */
.back-to-top {
  position: fixed;
  right: 24px;
  bottom: 24px;
  width: 44px;
  height: 44px;
  border-radius: 50%;
  background: var(--brand);
  color: var(--text);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.125rem;
  box-shadow: 0 4px 18px var(--brand-glow);
  opacity: 0;
  visibility: hidden;
  transition: var(--transition);
  z-index: 999;
}

.back-to-top.show {
  opacity: 1;
  visibility: visible;
}

.back-to-top:hover {
  background: var(--brand-light);
  transform: translateY(-3px);
}

/* ===== 滚动动效 ===== */
.fade-in {
  opacity: 0;
  transform: translateY(24px);
  transition: opacity 0.6s var(--ease), transform 0.6s var(--ease);
}

.fade-in.visible {
  opacity: 1;
  transform: translateY(0);
}

/* ===== 响应式 ===== */
@media (max-width: 1024px) {
  :root {
    --section-pad: 72px;
  }

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

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

  .footer-grid {
    grid-template-columns: 1fr 1fr;
    gap: 32px;
  }
}

@media (max-width: 768px) {
  :root {
    --section-pad: 56px;
  }

  .nav-links {
    position: fixed;
    top: 72px;
    left: 0;
    right: 0;
    flex-direction: column;
    align-items: flex-start;
    gap: 0;
    background: var(--bg-alt);
    border-bottom: 1px solid var(--border);
    padding: 12px 24px 20px;
    transform: translateY(-12px);
    opacity: 0;
    visibility: hidden;
    transition: var(--transition);
  }

  .nav-links.open {
    transform: translateY(0);
    opacity: 1;
    visibility: visible;
  }

  .nav-links a {
    width: 100%;
    padding: 12px 0;
    border-bottom: 1px solid var(--border);
  }

  .nav-links a.active::after {
    display: none;
  }

  .nav-cta {
    margin-top: 8px;
    text-align: center;
  }

  .menu-toggle {
    display: flex;
  }

  .hero {
    padding: 128px 0 56px;
  }

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

  .services-grid,
  .advantages-grid,
  .projects-grid,
  .cases-grid,
  .region-grid,
  .process-grid {
    grid-template-columns: 1fr;
  }

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

  .about-intro,
  .contact-grid {
    grid-template-columns: 1fr;
    gap: 32px;
  }

  .footer-grid {
    grid-template-columns: 1fr;
    gap: 28px;
  }

  .form-row {
    grid-template-columns: 1fr;
  }

  .cta-box {
    padding: 44px 20px;
  }
}

/* ===== 无障碍 ===== */
@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }

  .fade-in {
    opacity: 1;
    transform: none;
  }
}

:focus-visible {
  outline: 2px solid var(--brand);
  outline-offset: 3px;
  border-radius: 4px;
}