:root {
    --gradient-start: #2659F2;
    --gradient-end: #8C26E5;
    --accent-cyan: #00C8E0;
    --gold: #FAC714;
    --green: #27B373;
    --bg: #F2F2F7;
    --card-bg: #FFFFFF;
    --text-primary: #1C1C1E;
    --text-secondary: #6E6E73;
    --border: rgba(0, 0, 0, 0.08);
    --divider: rgba(0, 0, 0, 0.06);
}

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

html {
    scroll-behavior: smooth;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, "SF Pro Display", "Segoe UI", sans-serif;
    background: var(--bg);
    color: var(--text-primary);
    line-height: 1.6;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

/* Navigation */
.nav {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    z-index: 100;
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    background: rgba(255, 255, 255, 0.85);
    border-bottom: 1px solid var(--border);
}

.nav-inner {
    max-width: 720px;
    margin: 0 auto;
    padding: 14px 20px;
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.nav-brand {
    font-size: 20px;
    font-weight: 700;
    letter-spacing: -0.02em;
    background: linear-gradient(135deg, var(--gradient-start), var(--gradient-end));
    -webkit-background-clip: text;
    background-clip: text;
    -webkit-text-fill-color: transparent;
    text-decoration: none;
}

.nav-links {
    display: flex;
    gap: 24px;
}

.nav-links a {
    color: var(--text-primary);
    text-decoration: none;
    font-size: 15px;
    font-weight: 500;
    padding: 4px 0;
    position: relative;
}

.nav-links a:hover {
    color: var(--gradient-start);
}

.nav-links a.active {
    background: linear-gradient(135deg, var(--gradient-start), var(--gradient-end));
    -webkit-background-clip: text;
    background-clip: text;
    -webkit-text-fill-color: transparent;
}

.nav-links a.active::after {
    content: "";
    position: absolute;
    left: 0;
    right: 0;
    bottom: -2px;
    height: 2px;
    border-radius: 2px;
    background: linear-gradient(135deg, var(--gradient-start), var(--gradient-end));
}

/* Language toggle */
.lang-toggle {
    display: inline-flex;
    align-items: center;
    background: rgba(0, 0, 0, 0.05);
    border-radius: 999px;
    padding: 3px;
    margin-left: 16px;
}

.lang-toggle button {
    border: none;
    background: transparent;
    color: var(--text-secondary);
    font-family: inherit;
    font-size: 12px;
    font-weight: 600;
    letter-spacing: 0.04em;
    padding: 5px 12px;
    border-radius: 999px;
    cursor: pointer;
    transition: color 0.18s ease;
}

.lang-toggle button:hover {
    color: var(--text-primary);
}

.lang-toggle button.active {
    background: linear-gradient(135deg, var(--gradient-start), var(--gradient-end));
    color: #fff;
    box-shadow: 0 2px 6px rgba(38, 89, 242, 0.28);
}

/* Language section visibility — hide all lang blocks not matching body.lang-XX */
body.lang-vi [lang="en"],
body.lang-vi [lang="ja"],
body.lang-vi [lang="de"] {
    display: none !important;
}
body.lang-en [lang="vi"],
body.lang-en [lang="ja"],
body.lang-en [lang="de"] {
    display: none !important;
}
body.lang-ja [lang="vi"],
body.lang-ja [lang="en"],
body.lang-ja [lang="de"] {
    display: none !important;
}
body.lang-de [lang="vi"],
body.lang-de [lang="en"],
body.lang-de [lang="ja"] {
    display: none !important;
}

/* Hero */
.hero {
    background: linear-gradient(135deg, var(--gradient-start), var(--gradient-end));
    color: #fff;
    padding: 120px 20px 64px;
    text-align: center;
    border-radius: 0 0 32px 32px;
    margin-bottom: 32px;
}

.hero-icon {
    width: 52px;
    height: 52px;
    border-radius: 12px;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    box-shadow: 0 4px 14px rgba(38, 89, 242, 0.28);
    margin-bottom: 14px;
    overflow: hidden;
    background: #fff;
}

.hero-icon img {
    width: 100%;
    height: 100%;
    display: block;
    border-radius: 12px;
}

.hero h1 {
    font-size: 36px;
    font-weight: 700;
    letter-spacing: -0.03em;
    margin-bottom: 8px;
}

.hero-subtitle {
    font-size: 16px;
    opacity: 0.92;
    margin-bottom: 20px;
}

.badge {
    display: inline-block;
    background: rgba(255, 255, 255, 0.22);
    color: #fff;
    border-radius: 999px;
    padding: 6px 14px;
    font-size: 12px;
    font-weight: 600;
    letter-spacing: 0.02em;
    backdrop-filter: blur(8px);
    -webkit-backdrop-filter: blur(8px);
}

/* Content */
main {
    max-width: 720px;
    margin: 0 auto;
    padding: 0 20px 64px;
}

.card {
    background: var(--card-bg);
    border-radius: 20px;
    padding: 24px;
    box-shadow: 0 2px 12px rgba(0, 0, 0, 0.07);
    margin-bottom: 24px;
}

.card h2 {
    font-size: 24px;
    font-weight: 700;
    letter-spacing: -0.02em;
    margin-top: 28px;
    margin-bottom: 12px;
    background: linear-gradient(135deg, var(--gradient-start), var(--gradient-end));
    -webkit-background-clip: text;
    background-clip: text;
    -webkit-text-fill-color: transparent;
}

.card h2:first-child {
    margin-top: 0;
}

.card h3 {
    font-size: 17px;
    font-weight: 600;
    color: var(--text-primary);
    margin-top: 20px;
    margin-bottom: 8px;
}

.card h4 {
    font-size: 15px;
    font-weight: 600;
    color: var(--gradient-start);
    margin-top: 18px;
    margin-bottom: 6px;
}

.card p {
    color: var(--text-primary);
    margin-bottom: 12px;
    font-size: 15px;
}

.card ul {
    margin: 8px 0 16px 20px;
}

.card li {
    color: var(--text-primary);
    font-size: 15px;
    margin-bottom: 6px;
}

.card a {
    color: var(--gradient-start);
    text-decoration: none;
    font-weight: 500;
}

.card a:hover {
    text-decoration: underline;
}

.card hr {
    border: none;
    border-top: 1px solid var(--divider);
    margin: 36px 0;
}

/* Footer */
footer {
    background: #1C1C1E;
    color: rgba(255, 255, 255, 0.7);
    text-align: center;
    padding: 28px 20px;
    font-size: 13px;
}

footer a {
    color: rgba(255, 255, 255, 0.85);
    text-decoration: none;
}

footer a:hover {
    text-decoration: underline;
    color: #fff;
}

/* Mobile */
@media (max-width: 480px) {
    .hero {
        padding: 110px 20px 52px;
    }

    .hero h1 {
        font-size: 30px;
    }

    .card {
        padding: 20px;
        border-radius: 18px;
    }

    .card h2 {
        font-size: 21px;
    }

    .nav-links {
        gap: 14px;
    }

    .lang-toggle {
        margin-left: 10px;
    }

    .lang-toggle button {
        padding: 4px 9px;
        font-size: 11px;
    }
}