:root {
    --primary-color: #0f172a;
    --accent: #0284c7;
    --accent-light: #38bdf8;
    --accent-indigo: #6366f1;
    --text-color: #f8fafc;
    --text-secondary: #94a3b8;
    --bg-color: #0b1329;
    --secondary-bg: #1e293b;
    --card-bg: rgba(30, 41, 59, 0.7);
    --border: rgba(255, 255, 255, 0.1);
}

body {
    font-family: 'Inter', 'Noto Sans JP', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
    margin: 0;
    padding: 0;
    color: var(--text-color);
    background-color: var(--bg-color);
    line-height: 1.6;
}

nav {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 24px 0;
}

.nav-logo {
    display: flex;
    align-items: center;
    gap: 12px;
    font-weight: 800;
    font-size: 1.2rem;
}

.nav-logo img {
    width: 42px;
    height: 42px;
    border-radius: 10px;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);
}

.back-home {
    color: var(--text-secondary);
    text-decoration: none;
    transition: color 0.2s;
    font-weight: 500;
}

.back-home:hover {
    color: #fff;
}

.hero {
    text-align: center;
    max-width: 900px;
    margin: 0 auto;
    padding: 80px 0 90px;
}

.app-icon {
    width: 120px;
    height: 120px;
    border-radius: 26px;
    margin-bottom: 28px;
    box-shadow: 0 20px 50px rgba(0, 0, 0, 0.5), 0 0 30px rgba(2, 132, 199, 0.3);
}

.hero h1 {
    font-size: clamp(2.3rem, 6vw, 4.2rem);
    line-height: 1.18;
    margin-bottom: 24px;
    letter-spacing: -0.04em;
    font-weight: 800;
}

.hero h1 span {
    background: linear-gradient(135deg, #38bdf8, #818cf8);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
}

.hero .subtitle {
    color: var(--text-secondary);
    font-size: clamp(1rem, 2vw, 1.25rem);
    line-height: 1.9;
    margin-bottom: 36px;
}

.btn-download {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: 16px 36px;
    border-radius: 999px;
    background: linear-gradient(135deg, var(--accent), var(--accent-indigo));
    color: #fff;
    font-weight: 700;
    font-size: 1.1rem;
    text-decoration: none;
    box-shadow: 0 12px 30px rgba(2, 132, 199, 0.4);
    transition: transform 0.2s, box-shadow 0.2s;
}

.btn-download:hover {
    transform: translateY(-2px);
    box-shadow: 0 16px 40px rgba(2, 132, 199, 0.5);
}

.container {
    max-width: 1000px;
    margin: 0 auto;
    padding: 0 24px;
}

.section {
    margin-bottom: 100px;
}

.section h2 {
    font-size: clamp(1.8rem, 4vw, 2.6rem);
    margin-bottom: 24px;
    line-height: 1.3;
    color: #e2e8f0;
    letter-spacing: -0.02em;
}

.section > p {
    color: var(--text-secondary);
    line-height: 1.9;
    font-size: 1.05rem;
    margin-bottom: 20px;
}

.concept-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 20px;
    margin-top: 35px;
}

.concept-card {
    padding: 28px;
    border: 1px solid var(--border);
    background: var(--card-bg);
    border-radius: 20px;
    backdrop-filter: blur(12px);
}

.concept-card h3 {
    margin-top: 0;
    margin-bottom: 12px;
    font-size: 1.2rem;
    color: #f1f5f9;
}

.concept-card p {
    color: var(--text-secondary);
    line-height: 1.8;
    margin: 0;
    font-size: 0.95rem;
}

.learning-grid {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 20px;
    margin-top: 30px;
}

.learning-card {
    padding: 28px;
    border-radius: 20px;
    background: var(--card-bg);
    border: 1px solid var(--border);
    backdrop-filter: blur(12px);
}

.learning-card h3 {
    margin-top: 0;
    margin-bottom: 10px;
    font-size: 1.25rem;
    color: #38bdf8;
}

.learning-card p {
    color: var(--text-secondary);
    line-height: 1.8;
    margin: 0;
    font-size: 0.95rem;
}

.feature {
    display: grid;
    grid-template-columns: 1fr 340px;
    gap: 50px;
    align-items: center;
    padding: 45px 0;
    border-top: 1px solid var(--border);
}

.feature:last-child {
    border-bottom: 1px solid var(--border);
}

.feature-text h3 {
    margin: 0 0 14px;
    font-size: 1.5rem;
    color: #f1f5f9;
}

.feature-text p {
    color: var(--text-secondary);
    line-height: 1.85;
    font-size: 1rem;
}

.feature-image {
    text-align: center;
}

.feature-image img {
    max-width: 100%;
    width: 300px;
    border-radius: 22px;
    box-shadow: 0 20px 50px rgba(0, 0, 0, 0.6);
    border: 1px solid rgba(255, 255, 255, 0.12);
}

.steps {
    display: grid;
    gap: 18px;
    margin-top: 30px;
}

.step {
    display: flex;
    gap: 20px;
    padding: 24px;
    border-radius: 20px;
    background: var(--card-bg);
    border: 1px solid var(--border);
}

.step-number {
    flex: 0 0 44px;
    width: 44px;
    height: 44px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    background: linear-gradient(135deg, var(--accent), var(--accent-indigo));
    color: #fff;
    font-weight: 800;
}

.step h3 {
    margin: 0 0 8px;
    color: #f1f5f9;
}

.step p {
    color: var(--text-secondary);
    line-height: 1.8;
    margin: 0;
}

.use-case-grid {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 20px;
    margin-top: 30px;
}

.use-case {
    padding: 28px;
    border-radius: 20px;
    background: var(--card-bg);
    border: 1px solid var(--border);
}

.use-case h3 {
    margin-top: 0;
    margin-bottom: 10px;
    color: #f1f5f9;
}

.use-case p {
    color: var(--text-secondary);
    line-height: 1.8;
    margin: 0;
}

.faq-list {
    display: grid;
    gap: 14px;
    margin-top: 30px;
}

.faq-list details {
    border: 1px solid var(--border);
    border-radius: 16px;
    background: var(--card-bg);
    overflow: hidden;
}

.faq-list summary {
    cursor: pointer;
    padding: 20px 50px 20px 22px;
    font-weight: 700;
    line-height: 1.6;
    position: relative;
    list-style: none;
    color: #f1f5f9;
}

.faq-list summary::-webkit-details-marker {
    display: none;
}

.faq-list summary::after {
    content: '+';
    position: absolute;
    right: 20px;
    top: 50%;
    transform: translateY(-50%);
    font-size: 1.4rem;
    color: var(--accent-light);
}

.faq-list details[open] summary::after {
    content: '−';
}

.faq-answer {
    padding: 0 22px 22px;
    color: var(--text-secondary);
    line-height: 1.85;
}

.keywords {
    padding: 30px;
    border-radius: 20px;
    background: var(--card-bg);
    border: 1px solid var(--border);
}

.keywords h3 {
    margin-top: 0;
    color: #f1f5f9;
}

.keywords p {
    color: var(--text-secondary);
    line-height: 1.8;
    font-size: 0.9rem;
}

.final-cta {
    max-width: 900px;
    margin: 0 auto 100px;
    padding: 60px 30px;
    text-align: center;
    border-radius: 28px;
    background: linear-gradient(135deg, rgba(2, 132, 199, 0.15), rgba(99, 102, 241, 0.08));
    border: 1px solid var(--border);
}

.final-cta h2 {
    margin-bottom: 16px;
    color: #f1f5f9;
}

.final-cta p {
    color: var(--text-secondary);
    line-height: 1.8;
    margin-bottom: 28px;
}

footer {
    text-align: center;
    padding: 40px 0;
    border-top: 1px solid var(--border);
    color: var(--text-secondary);
    font-size: 0.9rem;
}

@media (max-width: 800px) {
    .hero {
        padding: 60px 0 70px;
    }
    .concept-grid, .learning-grid, .use-case-grid {
        grid-template-columns: 1fr;
    }
    .feature {
        grid-template-columns: 1fr;
        gap: 25px;
    }
    .feature-image {
        order: -1;
    }
}