/* ===== CSS Variables ===== */
:root {
  --primary: #2669bb;
  --primary-dark: #1a4f8f;
  --primary-light: #3d7fd4;
  --text-white: #ffffff;
  --text-dark: #1a1a2e;
  --text-muted: #555;
  --bg-light: #f9fafa;
  --bg-section: #eaedf0;
  --footer-bg: #102033;
  --header-height: 64px;
  --shadow: 0 2px 20px rgba(0, 0, 0, 0.12);
  --shadow-lg: 0 8px 32px rgba(0, 0, 0, 0.18);
  --radius: 8px;
  --transition: 0.3s ease;
  --font: 'Roboto Condensed', 'PingFang SC', 'Microsoft YaHei', sans-serif;
}

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

html {
  scroll-behavior: smooth;
  scroll-padding-top: calc(var(--header-height) + 16px);
}

body {
  font-family: var(--font);
  color: var(--text-dark);
  line-height: 1.6;
  overflow-x: hidden;
}

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

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

ul {
  list-style: none;
}

.container {
  width: 100%;
  max-width: 1140px;
  margin: 0 auto;
  padding: 0 20px;
}

/* ===== Header ===== */
.site-header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 1000;
  height: var(--header-height);
  background: var(--primary);
  transition: background var(--transition), box-shadow var(--transition);
}

.site-header.scrolled {
  background: rgba(38, 105, 187, 0.97);
  box-shadow: var(--shadow);
  backdrop-filter: blur(8px);
}

.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 100%;
  gap: 16px;
}

.logo-link {
  display: flex;
  align-items: center;
  gap: 10px;
  color: var(--text-white);
  flex-shrink: 0;
}

.logo-img {
  width: 36px;
  height: 36px;
  object-fit: contain;
}

.logo-text {
  font-size: 22px;
  font-weight: 700;
  letter-spacing: 0.05em;
}

.download-buttons {
  display: flex;
  gap: 12px;
  align-items: center;
  flex-shrink: 0;
}

.btn-download {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 10px 20px;
  border-radius: 24px;
  font-size: 15px;
  font-weight: 700;
  letter-spacing: 0.02em;
  transition: all var(--transition);
  white-space: nowrap;
  line-height: 1;
}

.btn-download .btn-icon {
  font-size: 20px;
  line-height: 1;
}

.btn-download .btn-icon-svg,
.btn-download .btn-icon-img {
  width: 22px;
  height: 22px;
  flex-shrink: 0;
}

.btn-android .btn-icon-img {
  filter: brightness(0) invert(1);
}

.btn-android:hover .btn-icon-img {
  filter: brightness(0) saturate(100%) invert(32%) sepia(67%) saturate(1200%) hue-rotate(186deg) brightness(92%) contrast(90%);
}

.btn-android {
  background: rgba(255, 255, 255, 0.15);
  color: var(--text-white);
  border: 1.5px solid rgba(255, 255, 255, 0.6);
}

.btn-android:hover {
  background: var(--text-white);
  color: var(--primary);
  transform: translateY(-1px);
}

.btn-ios {
  background: var(--text-white);
  color: var(--primary);
  border: 1.5px solid var(--text-white);
}

.btn-ios:hover {
  background: transparent;
  color: var(--text-white);
  transform: translateY(-1px);
}

/* ===== Hero ===== */
.hero {
  position: relative;
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  padding-top: var(--header-height);
}

.hero-bg {
  position: absolute;
  inset: 0;
  background-size: cover;
  background-position: center;
  background-attachment: fixed;
}

.hero-overlay {
  position: absolute;
  inset: 0;
  background: rgba(0, 0, 0, 0.45);
}

.hero-content {
  position: relative;
  z-index: 1;
  padding: 60px 20px;
}

.hero-title {
  font-size: clamp(42px, 8vw, 71px);
  font-weight: 700;
  color: var(--text-white);
  line-height: 1.1;
  margin-bottom: 16px;
  text-shadow: 0 2px 12px rgba(0, 0, 0, 0.3);
}

.hero-divider {
  width: 60px;
  height: 3px;
  background: var(--primary);
  margin: 0 auto 20px;
  border-radius: 2px;
}

.hero-subtitle {
  font-size: clamp(18px, 3.5vw, 26px);
  font-weight: 400;
  color: var(--text-white);
  opacity: 0.95;
  text-shadow: 0 1px 8px rgba(0, 0, 0, 0.25);
}

/* ===== Section Common ===== */
.section {
  position: relative;
  padding: 80px 0;
}

.section-title {
  font-size: clamp(28px, 5vw, 45px);
  font-weight: 700;
  text-align: center;
  margin-bottom: 12px;
}

.section-title-light {
  color: var(--text-white);
}

.section-title-dark {
  color: var(--text-dark);
}

.section-divider {
  width: 50px;
  height: 3px;
  background: var(--primary);
  margin: 0 auto 32px;
  border-radius: 2px;
}

.section-divider-light {
  background: var(--text-white);
}

.section-divider-dark {
  background: var(--primary);
}

/* ===== About ===== */
.about {
  min-height: 85vh;
  display: flex;
  align-items: center;
  background: var(--primary);
}

.about-bg {
  position: absolute;
  inset: 0;
  background-size: cover;
  background-position: center;
  opacity: 0.15;
}

.about-overlay {
  position: absolute;
  inset: 0;
  background: linear-gradient(135deg, rgba(38, 105, 187, 0.92) 0%, rgba(26, 79, 143, 0.88) 100%);
}

.about-content {
  position: relative;
  z-index: 1;
  text-align: center;
  max-width: 860px;
}

.about-content .section-title {
  color: var(--text-white);
}

.about-content .section-divider {
  background: rgba(255, 255, 255, 0.8);
}

.about-text {
  font-size: clamp(15px, 2.2vw, 18px);
  color: rgba(255, 255, 255, 0.92);
  line-height: 1.85;
  text-align: justify;
  text-align-last: center;
}

/* ===== Support ===== */
.support {
  min-height: 85vh;
  display: flex;
  align-items: center;
}

.support-bg {
  position: absolute;
  inset: 0;
  background-size: cover;
  background-position: center;
  background-attachment: fixed;
}

.support-overlay {
  position: absolute;
  inset: 0;
  background: rgba(0, 0, 0, 0.55);
}

.support-content {
  position: relative;
  z-index: 1;
  text-align: center;
}

.support-text {
  font-size: clamp(16px, 2.5vw, 22px);
  color: rgba(255, 255, 255, 0.9);
  max-width: 600px;
  margin: 0 auto;
}

/* ===== Services ===== */
.services {
  background: var(--bg-light);
  padding: 100px 0;
}

.services-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 32px;
  margin-top: 16px;
}

.service-card {
  background: var(--text-white);
  border-radius: 12px;
  padding: 36px 28px;
  text-align: center;
  box-shadow: 0 2px 12px rgba(0, 0, 0, 0.06);
  transition: transform var(--transition), box-shadow var(--transition);
  border-bottom: 3px solid transparent;
}

.service-card:hover {
  transform: translateY(-6px);
  box-shadow: var(--shadow-lg);
  border-bottom-color: var(--primary);
}

.service-icon {
  width: 96px;
  height: 96px;
  margin: 0 auto 20px;
  border-radius: 50%;
  overflow: hidden;
  box-shadow: 0 4px 16px rgba(38, 105, 187, 0.2);
}

.service-icon img {
  width: 100%;
  height: 100%;
  object-fit: cover;
}

.service-title {
  font-size: 20px;
  font-weight: 700;
  color: var(--text-dark);
  margin-bottom: 12px;
  line-height: 1.3;
}

.service-desc {
  font-size: 15px;
  color: var(--text-muted);
  line-height: 1.75;
}

/* ===== Footer ===== */
.site-footer {
  background: var(--footer-bg);
  padding: 32px 0;
}

.footer-inner {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 12px;
}

.footer-logo {
  width: 32px;
  height: 32px;
  object-fit: contain;
}

.footer-name {
  font-size: 20px;
  font-weight: 700;
  color: var(--text-white);
  letter-spacing: 0.05em;
}

/* ===== Back to Top ===== */
.back-to-top {
  position: fixed;
  bottom: 28px;
  right: 28px;
  width: 44px;
  height: 44px;
  border-radius: 50%;
  background: var(--primary);
  color: var(--text-white);
  border: none;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow: var(--shadow);
  opacity: 0;
  visibility: hidden;
  transform: translateY(12px);
  transition: all var(--transition);
  z-index: 900;
}

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

.back-to-top:hover {
  background: var(--primary-dark);
  transform: translateY(-2px);
}

/* ===== Responsive ===== */
@media (max-width: 992px) {
  .services-grid {
    grid-template-columns: repeat(2, 1fr);
    gap: 24px;
  }
}

@media (max-width: 768px) {
  :root {
    --header-height: 56px;
  }

  .hero-bg,
  .support-bg {
    background-attachment: scroll;
  }

  .download-buttons {
    gap: 8px;
  }

  .btn-download {
    padding: 8px 14px;
    font-size: 14px;
  }

  .btn-download .btn-icon {
    font-size: 18px;
  }

  .btn-download .btn-icon-svg,
  .btn-download .btn-icon-img {
    width: 18px;
    height: 18px;
  }

  .section {
    padding: 60px 0;
  }

  .about,
  .support {
    min-height: auto;
  }

  .services {
    padding: 60px 0;
  }

  .services-grid {
    grid-template-columns: 1fr;
    gap: 20px;
  }

  .service-card {
    padding: 28px 20px;
  }

  .about-text {
    text-align: left;
    text-align-last: left;
  }

  .back-to-top {
    bottom: 20px;
    right: 20px;
    width: 40px;
    height: 40px;
  }
}

@media (max-width: 480px) {
  .logo-text {
    font-size: 18px;
  }

  .logo-img {
    width: 30px;
    height: 30px;
  }

  .download-buttons {
    gap: 6px;
  }

  .btn-download {
    padding: 7px 12px;
    font-size: 13px;
  }

  .btn-download .btn-icon {
    font-size: 16px;
  }

  .btn-download .btn-icon-svg,
  .btn-download .btn-icon-img {
    width: 16px;
    height: 16px;
  }
}