* {
    box-sizing: border-box;
}

html,
body {
    margin: 0;
    padding: 0;
    font-family: system-ui, -apple-system, BlinkMacSystemFont, sans-serif;
    background: #f5f5f5;
}

.hidden {
    display: none;
}


/*  Navigation (All)  */

.nav {
    display: flex;
    justify-content: center;
    gap: 80px;
    padding: 24px 0;
    border-bottom: 1px solid #e0e0e0;
}

.nav a {
    text-decoration: none;
    color: #666;
    font-size: 17px;
}

.nav a.active {
    color: #111;
    border-bottom: 2px solid #bbb;
    padding-bottom: 6px;
}


/*  Shared Page Layout  */

.main {
    max-width: 1100px;
    margin: 80px auto;
    padding: 0 24px;
}

.sub {
    font-size: 16px;
    color: #666;
    margin-bottom: 40px;
}


/*  Introduction Page  */

.main.intro {
    max-width: 1000px;
}

.intro-hero {
    margin-bottom: 60px;
}

.intro-hero h1 {
    font-size: 56px;
    margin-bottom: 12px;
}

.intro-sub {
    font-size: 18px;
    color: #777;
}

.intro-text {
    margin-bottom: 50px;
}

.intro-text p {
    font-size: 20px;
}

.intro-split {
    display: grid;
    grid-template-columns: 1.1fr 0.9fr;
    gap: 48px;
    align-items: center;
    margin: 80px 0;
}

.introstext h2 {
    font-size: 28px;
    margin-bottom: 14px;
}

.introstext p {
    font-size: 20px;
    line-height: 2;
    color: #444;
}

.introsimage img {
    width: 100%;
    border-radius: 20px;
}

.intro-highlight {
    background: #ffffff;
    padding: 40px 48px;
    border-radius: 24px;
    margin: 80px 0;
    box-shadow: 0 12px 30px rgba(0, 0, 0, 0.06);
}

.intro-highlight p {
    font-size: 21px;
    line-height: 1.7;
    color: #222;
}


/*  How to Play Page  */

.howto-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 40px;
    margin-top: 60px;
}

.hblock {
    background: #ffffff;
    border-radius: 20px;
    padding: 28px;
    text-align: center;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.06);
}

.hblock img {
    width: 100%;
    margin-bottom: 24px;
}

.hblock h2 {
    font-size: 20px;
    margin-bottom: 12px;
}

.hblock p {
    font-size: 15px;
    line-height: 1.6;
    color: #444;
}


/*  Explanation Page  */

.main.explanation {
    max-width: 1100px;
}

.ex {
    margin-bottom: 80px;
}

.ex h2 {
    font-size: 28px;
    margin-bottom: 10px;
}

.ex .lead {
    font-size: 21px;
    color: #222;
    margin-bottom: 14px;
}

.ex p {
    font-size: 20px;
    color: #444;
}

.split {
    display: grid;
    grid-template-columns: 1.2fr 0.8fr;
    gap: 48px;
    align-items: center;
}

.split-image img {
    width: 100%;
    border-radius: 18px;
}

.mechanism-grid {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 40px;
    margin-top: 48px;
}

.mech-card {
    background: #ffffff;
    border-radius: 20px;
    padding: 26px 28px;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.05);
}

.mech-card h3 {
    font-size: 20px;
    margin: 18px 0 10px;
}

.mech-card p {
    font-size: 16px;
    color: #555;
}

.mech-visual {
    height: 140px;
    display: flex;
    align-items: center;
    justify-content: center;
}

.mech-visual img {
    max-width: 100%;
    max-height: 100%;
    object-fit: contain;
}