/* ============================================
   iter — minimal travel app site (metal-reflection style)
   ============================================ */

:root {
  --bg: #FFFFFF;
  --surface: #FAFAFC;
  --surface-elevated: #F2F2F7;
  --text: #1C1C1E;
  --text-secondary: #636366;
  --text-tertiary: #AEAEB2;
  --border: #E5E5EA;

  --metal-text: #3A3A3C;
  --metal-highlight: #48484A;
  --metal-light: #9C9CA3;
  --metal-shadow: rgba(28,28,30,0.04);

  --sp-xs: 4px;
  --sp-sm: 8px;
  --sp-md: 12px;
  --sp-base: 16px;
  --sp-lg: 24px;
  --sp-xl: 32px;
  --sp-xxl: 48px;

  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 12px;
  --radius-xl: 18px;

  --shimmer-duration: 550ms;
  --shimmer-angle: 47.5deg;
}

* { box-sizing: border-box; }

html {
  font-size: 16px;
  scroll-behavior: smooth;
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: 'SF Pro Text', 'SF Pro', -apple-system, BlinkMacSystemFont,
               'Helvetica Neue', 'Segoe UI', Roboto, 'PingFang SC',
               'Hiragino Sans', 'Yu Gothic', 'Noto Sans JP', 'Noto Sans KR',
               'Microsoft YaHei', sans-serif;
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

h1, h2, h3, h4 {
  font-family: 'SF Pro Display', 'SF Pro', -apple-system, BlinkMacSystemFont,
               'PingFang SC', 'Hiragino Sans', 'Yu Gothic', 'Noto Sans JP',
               'Noto Sans KR', 'Microsoft YaHei', sans-serif;
  font-weight: 800;
  letter-spacing: -0.02em;
  margin: 0;
}

h1 { font-size: 4rem; line-height: 1.05; font-weight: 800; }
h2 { font-size: 2.25rem; line-height: 1.1; font-weight: 800; }
h3 { font-size: 1.25rem; line-height: 1.2; font-weight: 700; }

p { margin: 0; }
a { color: inherit; text-decoration: none; }

/* ========================
   Top bar
   ======================== */
.topbar {
  position: sticky;
  top: 0;
  z-index: 50;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--sp-base) var(--sp-xl);
  background: rgba(255,255,255,0.85);
  backdrop-filter: saturate(180%) blur(20px);
  -webkit-backdrop-filter: saturate(180%) blur(20px);
  border-bottom: 1px solid var(--border);
}
.brand {
  display: inline-block;
  font-size: 1.5rem;
  font-weight: 800;
  letter-spacing: -0.02em;
}
.topbar nav {
  display: flex;
  gap: var(--sp-lg);
  align-items: center;
}
.topbar nav a {
  color: var(--text-secondary);
  font-size: 0.95rem;
}
.topbar nav a:hover { color: var(--metal-text); }
.lang-toggle {
  background: transparent;
  border: 1.5px solid var(--metal-highlight);
  border-radius: var(--radius-sm);
  padding: 4px 24px 4px 10px;
  font-family: inherit;
  font-size: 0.85rem;
  color: var(--metal-text);
  cursor: pointer;
  appearance: none;
  -webkit-appearance: none;
  background-image: url("data:image/svg+xml;utf8,<svg xmlns='http://www.w3.org/2000/svg' width='12' height='12' viewBox='0 0 12 12'><path d='M3 5l3 3 3-3' stroke='%23666' stroke-width='1.5' fill='none' stroke-linecap='round' stroke-linejoin='round'/></svg>");
  background-repeat: no-repeat;
  background-position: right 6px center;
}

/* ========================
   Sections
   ======================== */
main { padding: 0 var(--sp-xl); }

.hero, .features, .usecases, .download {
  max-width: 1100px;
  margin: 0 auto;
  padding: var(--sp-xxl) 0;
}

.hero { text-align: center; padding: 120px 0 80px; }
.hero-title {
  font-size: 6rem;
  letter-spacing: -0.04em;
  margin-bottom: var(--sp-base);
}
.hero-tag {
  font-size: 1.5rem;
  color: var(--text);
  font-weight: 600;
  margin-bottom: var(--sp-md);
  letter-spacing: -0.01em;
}
.hero-sub {
  font-size: 1.1rem;
  color: var(--text-secondary);
  margin-bottom: var(--sp-xl);
  max-width: 560px;
  margin-left: auto;
  margin-right: auto;
}
.hero-cta { display: flex; gap: var(--sp-md); justify-content: center; flex-wrap: wrap; }

.section-title {
  font-size: 2.25rem;
  margin-bottom: var(--sp-sm);
  text-align: center;
}
.section-sub {
  text-align: center;
  color: var(--text-secondary);
  margin-bottom: var(--sp-xl);
}

/* ========================
   Metal frame + shimmer
   ======================== */
.metal-frame {
  position: relative;
  background: var(--bg);
  border-radius: var(--radius-lg);
  isolation: isolate;
  overflow: hidden;
  border: 1.5px solid var(--metal-highlight);
}
.metal-frame::after {
  content: '';
  position: absolute;
  inset: 0;
  border-radius: inherit;
  background: linear-gradient(
    var(--shimmer-angle),
    rgba(255,255,255,0) 27.5%,
    rgba(255,255,255,0.85) 50%,
    rgba(255,255,255,0) 72.5%
  );
  transform: translateX(-150%);
  pointer-events: none;
  opacity: 0;
}
.metal-frame.shining::after {
  animation: shimmer-sweep var(--shimmer-duration) cubic-bezier(0.4, 0, 0.2, 1) forwards;
}
@keyframes shimmer-sweep {
  0%   { transform: translateX(-150%); opacity: 1; }
  75%  { transform: translateX(150%);  opacity: 1; }
  100% { transform: translateX(150%);  opacity: 0; }
}
.metal-text {
  position: relative;
  display: inline-block;
  color: var(--metal-text);
  isolation: isolate;
}
.metal-text::after {
  content: '';
  position: absolute;
  inset: 0;
  background: linear-gradient(
    var(--shimmer-angle),
    rgba(255,255,255,0) 27.5%,
    rgba(255,255,255,0.85) 50%,
    rgba(255,255,255,0) 72.5%
  );
  transform: translateX(-150%);
  pointer-events: none;
  opacity: 0;
}
.metal-text.shining::after {
  animation: shimmer-sweep var(--shimmer-duration) cubic-bezier(0.4, 0, 0.2, 1) forwards;
}

/* ========================
   Brand letters — 圆润字体 + 四字四色
   字体: Quicksand (web) / SF Pro Rounded (Apple) — 几何感、清新、边角圆润
   配色: i 海洋蓝 · t 落日橙 · e 森林绿 · r 朝霞粉
   ======================== */
.l-i, .l-t, .l-e, .l-r {
  font-family: 'PT Sans', -apple-system, BlinkMacSystemFont, sans-serif;
  font-weight: 700;
  letter-spacing: -0.02em;
}
.hero-title .l-i, .hero-title .l-t, .hero-title .l-e, .hero-title .l-r {
  font-weight: 700;
  letter-spacing: -0.04em;
}
/* Palette: No.13 "Crayon Box" — iOS 系统色, 蜡笔盒, 高饱和高明度 */
/* i 用纵向渐变: 点 = 夕阳红, 竖向下渐变到橙黄 */
.l-i {
  background: linear-gradient(
    to bottom,
    #FF3B30 0%,    /* 顶部(i 的点) — 落日红 */
    #FF5A2B 35%,   /* 竖的上段 — 暖橙红 */
    #FF8A1F 65%,   /* 竖的中段 — 橙 */
    #FFB800 100%   /* 竖的底部 — 橙黄 */
  );
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
  color: transparent;
}
.l-t { color: #0A84FF; }  /* iOS blue — 纯实色 */
.l-e { color: #FFD60A; }  /* iOS yellow */
.l-r { color: #30D158; }  /* iOS green */

/* ========================
   Store badge (App Store / Google Play, "Coming soon")
   ======================== */
.store-badge {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  padding: 10px 18px;
  background: var(--bg);
  color: var(--metal-text);
  font-weight: 600;
  font-size: 0.95rem;
  cursor: pointer;
  min-width: 180px;
  min-height: 56px;
  text-align: left;
  transition: transform 100ms ease;
}
.store-badge:hover { transform: translateY(-1px); }
.store-badge-icon {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 28px;
  color: var(--metal-text);
}
.store-badge-text {
  display: inline-flex;
  flex-direction: column;
  justify-content: center;
  line-height: 1.1;
}
.store-badge-top {
  font-size: 0.7rem;
  font-weight: 500;
  color: var(--text-tertiary);
  text-transform: uppercase;
  letter-spacing: 0.06em;
}
.store-badge-bot {
  font-size: 1.05rem;
  font-weight: 700;
  color: var(--metal-text);
  letter-spacing: -0.01em;
}

/* ========================
   Features
   ======================== */
.features {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--sp-lg);
  max-width: 1100px;
  margin: 0 auto;
  padding: var(--sp-xxl) var(--sp-base);
}
.feature-card {
  display: flex;
  flex-direction: column;
  align-items: center;
  text-align: center;
  gap: var(--sp-sm);
  padding: var(--sp-base);
  background: transparent;
}
.feature-icon { font-size: 2.5rem; flex-shrink: 0; }
.feature-body h3 { font-size: 1rem; font-weight: 700; margin-bottom: 2px; }
.feature-body p { font-size: 0.9rem; color: var(--text-secondary); }

/* ========================
   Use cases
   ======================== */
.usecases {
  max-width: 1100px;
  margin: 0 auto;
  padding: var(--sp-xxl) var(--sp-base);
}
.usecase-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--sp-lg);
  margin-top: var(--sp-lg);
}
.usecase-card {
  padding: var(--sp-lg);
  display: flex;
  flex-direction: column;
  gap: var(--sp-sm);
  background: transparent;
}
.usecase-icon { font-size: 2.5rem; }
.usecase-card h3 { font-size: 1.05rem; font-weight: 700; }
.usecase-card p { font-size: 0.92rem; line-height: 1.6; color: var(--text-secondary); }

/* ========================
   Download
   ======================== */
.download { text-align: center; }
.download p { color: var(--text-secondary); margin-bottom: var(--sp-xl); max-width: 520px; margin-left: auto; margin-right: auto; }
.download-cta { display: flex; gap: var(--sp-md); justify-content: center; flex-wrap: wrap; margin-bottom: var(--sp-lg); }
.download-note { font-size: 0.9rem; color: var(--text-tertiary); }
.download-note a { color: var(--metal-text); border-bottom: 1px solid var(--border); }

/* ========================
   Footer
   ======================== */
footer {
  margin-top: var(--sp-xxl);
  padding: var(--sp-xl) var(--sp-xl);
  border-top: 1px solid var(--border);
  background: var(--surface);
}
.footer-inner {
  max-width: 1100px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: var(--sp-md);
}
.footer-brand { font-size: 1rem; font-weight: 800; letter-spacing: -0.02em; }
.footer-inner nav { display: flex; gap: var(--sp-base); }
.footer-inner nav a { color: var(--text-secondary); font-size: 0.85rem; }
.footer-inner nav a:hover { color: var(--metal-text); }
.footer-copy { color: var(--text-tertiary); font-size: 0.8rem; }

/* ========================
   Responsive
   ======================== */
@media (max-width: 1000px) {
  .features {
    grid-template-columns: repeat(2, 1fr);
    max-width: 720px;
    margin: 0 auto;
  }
  .usecase-grid {
    grid-template-columns: 1fr;
    max-width: 600px;
    margin-left: auto;
    margin-right: auto;
  }
}
@media (max-width: 600px) {
  h1 { font-size: 3rem; }
  h2 { font-size: 1.75rem; }
  .hero-title { font-size: 4.5rem; }
  .hero-tag { font-size: 1.2rem; }
  .hero-sub { font-size: 1rem; }
  main { padding: 0 var(--sp-base); }
  .topbar { padding: var(--sp-md) var(--sp-base); }
  .topbar nav { gap: var(--sp-md); }
  .features { grid-template-columns: 1fr; max-width: 480px; }
  .feature-card {
    flex-direction: row;
    text-align: left;
    align-items: center;
    gap: var(--sp-base);
  }
  .feature-icon { font-size: 2rem; width: 44px; }
  .store-badge { min-width: 160px; padding: 10px 14px; }
  .footer-inner { flex-direction: column; text-align: center; }
}