:root {
  --color-bg: #ffffff;
  --color-surface: #f7f7f9;
  --color-surface-hover: #eeeef2;
  --color-border: #e4e4e8;
  --color-text: #1a1a1f;
  --color-text-muted: #5a5a66;
  --color-primary: #4b4bff;
  --color-primary-hover: #3838d6;
  --color-primary-contrast: #ffffff;
  --color-accent: #ff9059;
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.04);
  --shadow-md: 0 6px 24px rgba(0, 0, 0, 0.06);
  --max-width: 1080px;
  --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC",
    "Hiragino Sans GB", "Microsoft YaHei", "Helvetica Neue", Helvetica, Arial,
    sans-serif;
  --font-mono: ui-monospace, SFMono-Regular, "SF Mono", Consolas,
    "Liberation Mono", Menlo, monospace;
}

@media (prefers-color-scheme: dark) {
  :root {
    --color-bg: #101014;
    --color-surface: #18181e;
    --color-surface-hover: #22222b;
    --color-border: #2a2a34;
    --color-text: #f2f2f5;
    --color-text-muted: #a0a0ae;
    --color-primary: #7f7fff;
    --color-primary-hover: #9b9bff;
    --color-primary-contrast: #101014;
    --color-accent: #ffb28a;
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.3);
    --shadow-md: 0 6px 24px rgba(0, 0, 0, 0.4);
  }
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  font-family: var(--font-sans);
  font-size: 16px;
  line-height: 1.6;
  color: var(--color-text);
  background: var(--color-bg);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

a {
  color: var(--color-primary);
  text-decoration: none;
}

a:hover {
  text-decoration: underline;
}

code {
  font-family: var(--font-mono);
  font-size: 0.92em;
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  padding: 0.1em 0.4em;
  border-radius: var(--radius-sm);
}

h1,
h2,
h3 {
  margin: 0 0 0.5em;
  line-height: 1.25;
  color: var(--color-text);
}

h1 {
  font-size: clamp(2rem, 4vw, 3rem);
  letter-spacing: -0.02em;
}

h2 {
  font-size: clamp(1.5rem, 2.8vw, 2rem);
  letter-spacing: -0.01em;
}

h3 {
  font-size: 1.125rem;
}

p {
  margin: 0 0 1em;
  color: var(--color-text);
}

.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 24px;
}

/* Nav */
.site-nav {
  border-bottom: 1px solid var(--color-border);
  background: var(--color-bg);
  position: sticky;
  top: 0;
  z-index: 10;
  backdrop-filter: saturate(1.4) blur(6px);
}

.site-nav .container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding-top: 14px;
  padding-bottom: 14px;
}

.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  font-weight: 600;
  color: var(--color-text);
}

.brand img {
  width: 28px;
  height: 28px;
  border-radius: 6px;
}

.brand-name {
  font-size: 1.05rem;
  letter-spacing: 0.01em;
}

.lang-switch {
  font-size: 0.9rem;
  color: var(--color-text-muted);
}

.lang-switch a {
  color: var(--color-text-muted);
}

.lang-switch a.active {
  color: var(--color-text);
  font-weight: 600;
}

.lang-switch .sep {
  margin: 0 8px;
  opacity: 0.4;
}

/* Hero */
.hero {
  padding: 72px 0 56px;
  text-align: center;
}

.hero .logo-lg {
  width: 88px;
  height: 88px;
  border-radius: 20px;
  box-shadow: var(--shadow-md);
  margin-bottom: 24px;
}

.hero .tagline {
  font-size: clamp(1.05rem, 1.6vw, 1.2rem);
  color: var(--color-text-muted);
  max-width: 640px;
  margin: 0 auto 32px;
}

.cta-row {
  display: flex;
  gap: 12px;
  justify-content: center;
  flex-wrap: wrap;
}

.btn {
  display: inline-block;
  padding: 12px 22px;
  border-radius: var(--radius-md);
  font-weight: 600;
  font-size: 0.98rem;
  border: 1px solid transparent;
  transition:
    background 0.15s ease,
    border-color 0.15s ease,
    color 0.15s ease;
  cursor: pointer;
}

.btn:hover {
  text-decoration: none;
}

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

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

.btn-secondary {
  background: var(--color-surface);
  color: var(--color-text);
  border-color: var(--color-border);
}

.btn-secondary:hover {
  background: var(--color-surface-hover);
}

.cta-note {
  margin-top: 14px;
  font-size: 0.85rem;
  color: var(--color-text-muted);
}

/* Sections */
section {
  padding: 56px 0;
}

.section-title {
  text-align: center;
  margin-bottom: 40px;
}

.section-title p {
  color: var(--color-text-muted);
  max-width: 620px;
  margin: 8px auto 0;
}

/* Features grid */
.features {
  display: grid;
  grid-template-columns: 1fr;
  gap: 16px;
}

@media (min-width: 640px) {
  .features {
    grid-template-columns: repeat(2, 1fr);
  }
}

@media (min-width: 960px) {
  .features {
    grid-template-columns: repeat(3, 1fr);
  }
}

.feature-card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 22px;
  box-shadow: var(--shadow-sm);
}

.feature-card h3 {
  margin-bottom: 8px;
}

.feature-card p {
  margin: 0;
  color: var(--color-text-muted);
  font-size: 0.95rem;
}

/* Steps */
.steps {
  counter-reset: step;
  display: grid;
  gap: 14px;
  max-width: 720px;
  margin: 0 auto;
}

.step {
  display: flex;
  gap: 16px;
  padding: 18px 20px;
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
}

.step-num {
  flex: 0 0 32px;
  width: 32px;
  height: 32px;
  border-radius: 50%;
  background: var(--color-primary);
  color: var(--color-primary-contrast);
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: 0.95rem;
}

.step-body {
  flex: 1;
}

.step-body strong {
  display: block;
  margin-bottom: 2px;
}

.step-body p {
  margin: 0;
  color: var(--color-text-muted);
  font-size: 0.95rem;
}

/* Privacy callout */
.privacy-callout {
  max-width: 720px;
  margin: 0 auto;
  padding: 28px;
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  text-align: center;
}

.privacy-callout p {
  color: var(--color-text-muted);
  margin-bottom: 16px;
}

/* Footer */
.site-footer {
  border-top: 1px solid var(--color-border);
  padding: 32px 0 48px;
  font-size: 0.9rem;
  color: var(--color-text-muted);
}

.site-footer .container {
  display: flex;
  flex-wrap: wrap;
  gap: 16px;
  justify-content: space-between;
  align-items: center;
}

.footer-links {
  display: flex;
  gap: 18px;
  flex-wrap: wrap;
}

.footer-links a {
  color: var(--color-text-muted);
}

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

/* Doc pages (privacy) */
.doc {
  padding: 56px 0 80px;
}

.doc-inner {
  max-width: 760px;
  margin: 0 auto;
}

.doc h1 {
  margin-bottom: 8px;
}

.doc .effective-date {
  color: var(--color-text-muted);
  font-size: 0.95rem;
  margin-bottom: 32px;
}

.doc h2 {
  margin-top: 40px;
  padding-top: 8px;
  font-size: 1.25rem;
}

.doc h3 {
  margin-top: 24px;
  font-size: 1.05rem;
}

.doc ul {
  padding-left: 1.2em;
  margin: 0 0 1em;
}

.doc li {
  margin-bottom: 0.4em;
}

.doc .back-link {
  display: inline-block;
  margin-bottom: 32px;
  font-size: 0.9rem;
}