:root {
    /* Navy-Gray Base */
    --bg-deep: #0d1220;
    --bg-primary: #141c2e;
    --bg-secondary: #1a2540;
    --bg-tertiary: #243051;

    /* Accent Blues */
    --accent-primary: #5a7eb8;
    --accent-secondary: #8aa8d4;
    --accent-glow: rgba(90, 126, 184, 0.15);

    /* Text Colors */
    --text-primary: #e4e8f0;
    --text-secondary: #9aa3b8;
    --text-muted: #6b7590;

    /* Decorative */
    --border-subtle: rgba(138, 168, 212, 0.12);
}

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

html {
    scroll-behavior: smooth;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Hiragino Sans', 'Hiragino Kaku Gothic ProN', 'Yu Gothic', sans-serif;
    background: var(--bg-deep);
    min-height: 100vh;
    color: var(--text-primary);
    line-height: 1.85;
    overflow-x: hidden;
    position: relative;
}

/* Mesh Gradient Background */
.mesh-bg {
    position: fixed;
    inset: 0;
    background:
        radial-gradient(ellipse 80% 60% at 15% 20%, rgba(58, 90, 140, 0.25) 0%, transparent 55%),
        radial-gradient(ellipse 70% 50% at 85% 15%, rgba(70, 100, 150, 0.18) 0%, transparent 50%),
        radial-gradient(ellipse 90% 70% at 50% 90%, rgba(50, 80, 130, 0.2) 0%, transparent 60%),
        radial-gradient(ellipse 60% 40% at 75% 60%, rgba(80, 110, 160, 0.12) 0%, transparent 45%),
        radial-gradient(ellipse 50% 35% at 25% 70%, rgba(60, 95, 145, 0.15) 0%, transparent 50%),
        linear-gradient(175deg, var(--bg-deep) 0%, var(--bg-primary) 40%, var(--bg-secondary) 100%);
    z-index: 0;
}

/* Cloud Layer */
.cloud-layer {
    position: fixed;
    inset: 0;
    pointer-events: none;
    z-index: 1;
    overflow: hidden;
}

.cloud {
    position: absolute;
    filter: blur(12px);
}

.cloud-1 {
    width: 650px;
    height: 260px;
    top: 0%;
    animation: drift var(--duration-1, 75s) linear infinite;
    animation-delay: var(--delay-1, 0s);
    opacity: 1;
}

.cloud-2 {
    width: 500px;
    height: 290px;
    top: 5%;
    animation: drift var(--duration-2, 55s) linear infinite;
    animation-delay: var(--delay-2, 0s);
    opacity: 0.9;
}

.cloud-3 {
    width: 600px;
    height: 240px;
    top: 2%;
    animation: drift var(--duration-3, 90s) linear infinite;
    animation-delay: var(--delay-3, 0s);
    opacity: 0.85;
}

@keyframes drift {
    from { transform: translateX(-100%); }
    to { transform: translateX(calc(100vw + 100%)); }
}

/* Container */
.container {
    max-width: 720px;
    margin: 0 auto;
    padding: 60px 28px 100px;
    position: relative;
    z-index: 2;
}

/* Language Navigation */
.lang-nav {
    position: absolute;
    top: 20px;
    right: 28px;
    font-size: 0.85rem;
    z-index: 10;
}

.lang-nav a {
    color: var(--text-secondary);
    text-decoration: none;
    padding: 4px 8px;
    border-radius: 4px;
    transition: color 0.2s ease, background-color 0.2s ease;
}

.lang-nav a:hover {
    color: var(--text-primary);
    background-color: var(--accent-glow);
}

.lang-nav a.active {
    color: var(--text-primary);
    font-weight: 600;
    border-bottom: 2px solid var(--accent-primary);
}

.lang-nav .separator {
    color: var(--text-muted);
    margin: 0 4px;
}

/* Header */
.header {
    text-align: center;
    margin-bottom: 80px;
    opacity: 0;
    animation: fade-in 1s ease-out 0.2s forwards;
}

.app-icon {
    width: 72px;
    height: 72px;
    margin: 0 auto 24px;
    display: flex;
    align-items: center;
    justify-content: center;
}

.app-icon img {
    width: 100%;
    height: 100%;
    border-radius: 16px;
    filter: drop-shadow(0 4px 20px rgba(138, 168, 212, 0.3));
}

.app-name {
    font-size: 2.2rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 8px;
    letter-spacing: 0.04em;
}

.subtitle {
    font-size: 0.95rem;
    color: var(--text-secondary);
    font-weight: 400;
    letter-spacing: 0.08em;
    text-transform: uppercase;
}

/* Content Sections */
main {
    display: flex;
    flex-direction: column;
    gap: 48px;
}

section {
    opacity: 0;
    transform: translateY(24px);
    animation: slide-up 0.7s ease-out forwards;
}

section:nth-child(1) { animation-delay: 0.3s; }
section:nth-child(2) { animation-delay: 0.4s; }
section:nth-child(3) { animation-delay: 0.5s; }
section:nth-child(4) { animation-delay: 0.6s; }
section:nth-child(5) { animation-delay: 0.7s; }
section:nth-child(6) { animation-delay: 0.8s; }
section:nth-child(7) { animation-delay: 0.9s; }

@keyframes slide-up {
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

@keyframes fade-in {
    to { opacity: 1; }
}

h2 {
    font-size: 1.25rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 20px;
    display: flex;
    align-items: center;
    gap: 14px;
    letter-spacing: 0.02em;
}

h2::before {
    content: '';
    display: block;
    width: 3px;
    height: 22px;
    background: linear-gradient(180deg, var(--accent-primary) 0%, var(--accent-secondary) 100%);
    border-radius: 2px;
    flex-shrink: 0;
}

h3 {
    font-size: 1rem;
    font-weight: 500;
    color: var(--text-primary);
    margin: 28px 0 14px;
    padding-left: 17px;
}

p {
    margin-bottom: 16px;
    color: var(--text-secondary);
    font-size: 0.95rem;
}

.highlight {
    background: var(--accent-glow);
    border-left: 2px solid var(--accent-primary);
    padding: 16px 20px;
    border-radius: 0 8px 8px 0;
    margin: 20px 0;
}

.highlight p {
    margin: 0;
    color: var(--text-primary);
}

.highlight strong {
    color: var(--accent-secondary);
}

ul {
    list-style: none;
    padding: 0;
    margin: 0;
}

li {
    padding: 10px 0 10px 32px;
    position: relative;
    color: var(--text-secondary);
    font-size: 0.95rem;
}

li::before {
    content: '';
    position: absolute;
    left: 8px;
    top: 18px;
    width: 6px;
    height: 6px;
    background: var(--accent-primary);
    border-radius: 50%;
    opacity: 0.7;
}

li strong {
    color: var(--text-primary);
    font-weight: 500;
}

a {
    color: var(--accent-secondary);
    text-decoration: none;
    font-weight: 400;
    transition: color 0.2s ease;
    border-bottom: 1px solid transparent;
}

a:hover {
    color: var(--text-primary);
    border-bottom-color: var(--accent-secondary);
}

/* Section Divider */
section + section {
    padding-top: 48px;
    border-top: 1px solid var(--border-subtle);
}

/* Contact Section */
.contact-info {
    text-align: center;
    padding: 24px 0 0;
}

.contact-info p {
    margin-bottom: 10px;
}

.support-note {
    font-size: 0.85rem;
    color: var(--text-muted);
    font-style: italic;
    margin-top: 16px;
}

/* Footer */
.footer {
    text-align: center;
    margin-top: 80px;
    padding: 32px 0;
    color: var(--text-muted);
    font-size: 0.85rem;
    opacity: 0;
    animation: fade-in 1s ease-out 1.2s forwards;
}

/* Responsive */
@media (max-width: 768px) {
    .container {
        padding: 40px 20px 80px;
    }

    .lang-nav {
        top: 12px;
        right: 20px;
        font-size: 0.8rem;
    }

    .header {
        margin-bottom: 60px;
    }

    .app-icon {
        width: 60px;
        height: 60px;
    }

    .app-name {
        font-size: 1.8rem;
    }

    .subtitle {
        font-size: 0.85rem;
    }

    main {
        gap: 36px;
    }

    section + section {
        padding-top: 36px;
    }

    h2 {
        font-size: 1.15rem;
    }

    .cloud-1 {
        width: 420px;
        height: 170px;
    }

    .cloud-2 {
        width: 320px;
        height: 185px;
    }

    .cloud-3 {
        width: 380px;
        height: 150px;
    }

    .cloud {
        filter: blur(10px);
    }
}

@media (max-width: 480px) {
    .cloud {
        filter: blur(8px);
    }

    .cloud-1 { width: 300px; height: 120px; opacity: 0.9; }
    .cloud-2 { width: 240px; height: 140px; opacity: 0.85; }
    .cloud-3 { width: 280px; height: 110px; opacity: 0.8; }
}

/* Reduced Motion */
@media (prefers-reduced-motion: reduce) {
    .cloud {
        animation: none;
        left: 10%;
    }

    .cloud-2 {
        left: 40%;
    }

    .cloud-3 {
        left: 60%;
    }

    section {
        animation: none;
        opacity: 1;
        transform: none;
    }

    .header {
        animation: none;
        opacity: 1;
    }

    .footer {
        animation: none;
        opacity: 1;
    }
}