/* ========== 全局基础 ========== */
html {
  scroll-behavior: smooth;
  scroll-padding-top: 6rem;
}

body {
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

::selection {
  background: #165DFF;
  color: #fff;
}

::-webkit-scrollbar {
  width: 8px;
  height: 8px;
}
::-webkit-scrollbar-track {
  background: #f1f5f9;
}
::-webkit-scrollbar-thumb {
  background: #cbd5e1;
  border-radius: 999px;
}
::-webkit-scrollbar-thumb:hover {
  background: #165DFF;
}

/* ========== 导航链接下划线动效 ========== */
.nav-link {
  position: relative;
  color: #475569;
  font-weight: 500;
  padding: 4px 0;
  transition: color 0.2s ease;
}
.nav-link:hover,
.nav-link.active {
  color: #165DFF;
}
.nav-link::after {
  content: '';
  position: absolute;
  left: 0;
  bottom: -4px;
  width: 0;
  height: 2px;
  border-radius: 2px;
  background: #165DFF;
  transition: width 0.25s ease;
}
.nav-link:hover::after,
.nav-link.active::after {
  width: 100%;
}

/* ========== 汉堡按钮 ========== */
#menu-btn span {
  display: block;
  width: 22px;
  height: 2px;
  border-radius: 2px;
  background: #0f172a;
  transition: transform 0.3s ease, opacity 0.3s ease;
}
#menu-btn span + span {
  margin-top: 5px;
}
#menu-btn.open span:nth-child(1) {
  transform: translateY(7px) rotate(45deg);
}
#menu-btn.open span:nth-child(2) {
  opacity: 0;
}
#menu-btn.open span:nth-child(3) {
  transform: translateY(-7px) rotate(-45deg);
}

/* ========== 移动端菜单展开动画 ========== */
#mobile-menu {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.35s ease;
}
#mobile-menu.open {
  max-height: 430px;
}

/* ========== 滚动入场动画 ========== */
.reveal {
  opacity: 0;
  transform: translateY(28px);
  transition: opacity 0.6s ease, transform 0.6s ease;
  will-change: opacity, transform;
}
.reveal.visible {
  opacity: 1;
  transform: translateY(0);
}
.reveal-delay-1 {
  transition-delay: 0.12s;
}
.reveal-delay-2 {
  transition-delay: 0.24s;
}
.reveal-delay-3 {
  transition-delay: 0.36s;
}

/* ========== 回到顶部按钮 ========== */
#back-top {
  opacity: 0;
  pointer-events: none;
  transform: translateY(12px);
  transition: opacity 0.3s ease, transform 0.3s ease;
}
#back-top.show {
  opacity: 1;
  pointer-events: auto;
  transform: translateY(0);
}