/* Twitter官网入口 - 变量与基础 */
:root {
  --color-dark: #2c3e50;
  --color-accent: #3498db;
  --color-accent-hover: #2980b9;
  --color-text: #2c3e50;
  --color-text-muted: #5d6d7e;
  --color-border: #ecf0f1;
  --color-white: #ffffff;
  --font-sans: "PingFang SC", "Microsoft YaHei", "Helvetica Neue", Arial, sans-serif;
  --space-xs: 0.5rem;
  --space-sm: 1rem;
  --space-md: 1.5rem;
  --space-lg: 2rem;
  --space-xl: 3rem;
  --space-2xl: 4rem;
  --radius-sm: 4px;
  --radius-md: 8px;
  --radius-pill: 9999px;
  --transition: 0.2s ease;
}

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

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

body {
  font-family: var(--font-sans);
  color: var(--color-text);
  background: var(--color-white);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}

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

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

/* Header */
.header {
  background: var(--color-dark);
  padding: var(--space-md) var(--space-lg);
  text-align: center;
}

.header__title {
  color: var(--color-white);
  font-size: 1.25rem;
  font-weight: 700;
}

/* Hero */
.hero {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--space-2xl);
  align-items: center;
  max-width: 1200px;
  margin: 0 auto;
  padding: var(--space-2xl) var(--space-lg);
}

.hero__title {
  font-size: 2.25rem;
  font-weight: 700;
  color: var(--color-text);
  line-height: 1.3;
  margin-bottom: var(--space-md);
}

.hero__desc {
  color: var(--color-text-muted);
  font-size: 1rem;
  margin-bottom: var(--space-lg);
}

.hero__actions {
  display: flex;
  gap: var(--space-sm);
  flex-wrap: wrap;
}

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: var(--space-sm) var(--space-lg);
  font-size: 0.9375rem;
  font-weight: 500;
  border-radius: var(--radius-pill);
  cursor: pointer;
  transition: background var(--transition), border-color var(--transition), color var(--transition);
}

.btn--outline {
  background: var(--color-white);
  border: 2px solid #bdc3c7;
  color: var(--color-text);
}

.btn--outline:hover {
  border-color: #95a5a6;
  background: #f8f9fa;
}

.btn--primary {
  background: var(--color-accent);
  border: none;
  color: var(--color-white);
}

.btn--primary:hover {
  background: var(--color-accent-hover);
}

/* Hero Visual */
.hero__visual {
  display: flex;
  justify-content: center;
  align-items: center;
}

.hero__card-img {
  width: 100%;
  max-width: 560px;
  height: auto;
  border-radius: var(--radius-md);
  box-shadow: 0 10px 40px rgba(52, 152, 219, 0.25);
  object-fit: cover;
}

.hero__card {
  width: 100%;
  max-width: 400px;
  aspect-ratio: 4/3;
  border-radius: var(--radius-md);
  background: linear-gradient(135deg, #6dd5ed 0%, #a8b5e8 35%, #5bc0de 70%, #2193b0 100%);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  box-shadow: 0 10px 40px rgba(52, 152, 219, 0.25);
}

.hero__card-brand {
  font-size: 2.5rem;
  font-weight: 700;
  color: var(--color-white);
  text-shadow: 0 2px 4px rgba(0, 0, 0, 0.15);
  margin-bottom: var(--space-xs);
}

.hero__card-tagline {
  font-size: 1rem;
  color: rgba(255, 255, 255, 0.95);
  font-weight: 500;
}

/* Features */
.features {
  max-width: 1200px;
  margin: 0 auto;
  padding: var(--space-2xl) var(--space-lg);
}

.features__title {
  font-size: 1.75rem;
  font-weight: 700;
  text-align: center;
  margin-bottom: var(--space-xl);
  color: var(--color-text);
}

.features__grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--space-lg);
}

.feature-card {
  background: var(--color-white);
  border: 2px solid #bdc3c7;
  border-radius: var(--radius-md);
  padding: var(--space-xl);
  text-align: center;
  transition: box-shadow var(--transition), border-color var(--transition);
}

.feature-card:hover {
  border-color: #95a5a6;
  box-shadow: 0 4px 20px rgba(0, 0, 0, 0.06);
}

.feature-card__icon {
  display: flex;
  justify-content: center;
  margin-bottom: var(--space-md);
  font-size: 48px;
  line-height: 1;
}

.feature-card__title {
  font-size: 1.125rem;
  font-weight: 700;
  color: var(--color-text);
  margin-bottom: var(--space-sm);
}

.feature-card__desc {
  font-size: 0.875rem;
  color: var(--color-text-muted);
  line-height: 1.65;
}

/* Footer */
.footer {
  background: var(--color-dark);
  padding: var(--space-xl) var(--space-lg);
  text-align: center;
  color: var(--color-white);
}

.footer__copyright {
  font-size: 0.875rem;
  margin-bottom: var(--space-xs);
}

.footer__links {
  font-size: 0.875rem;
}

.footer__links a {
  color: rgba(255, 255, 255, 0.9);
  transition: color var(--transition);
}

.footer__links a:hover {
  color: var(--color-white);
}

/* Responsive */
@media (max-width: 768px) {
  .hero {
    grid-template-columns: 1fr;
    padding: var(--space-xl) var(--space-md);
  }

  .hero__visual {
    order: -1;
  }

  .hero__title {
    font-size: 1.75rem;
  }

  .features__grid {
    grid-template-columns: 1fr;
  }

  .feature-card {
    padding: var(--space-lg);
  }
}