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

body {
    background: #f4f6fb;
    color: #1f2937;
    font-family: Arial, Helvetica, sans-serif;
    min-height: 100vh;
}

.back-button {
    position: fixed;
    top: 24px;
    left: 24px;

    text-decoration: none;
    color: #111827;

    background: white;
    padding: 12px 18px;
    border-radius: 12px;

    box-shadow: 0 6px 18px rgba(0, 0, 0, 0.08);
    transition: 0.25s;
    z-index: 10;
}

.back-button:hover {
    transform: translateY(-2px);
    background: #111827;
    color: white;
}

.article-container {
    width: min(92%, 980px);
    margin: 60px auto;
}

.article-card {
    background: white;
    padding: 48px;
    border-radius: 24px;
    box-shadow: 0 15px 35px rgba(0, 0, 0, 0.08);
}

.article-date {
    text-align: center;
    color: #6b7280;
    font-size: 15px;
    margin-bottom: 12px;
}

.article-title {
    text-align: center;
    font-size: 42px;
    line-height: 1.2;
    margin-bottom: 32px;
    color: #111827;
}

.article-text {
    text-align: center;
    font-size: 18px;
    line-height: 1.7;
    margin: 25px 0;
}

.math-box {
    background: #f8fafc;
    border: 1px solid #e5e7eb;
    border-radius: 18px;

    padding: 22px;
    margin: 24px 0;

    overflow-x: auto;
}

h2 {
    text-align: center;
    font-size: 26px;
    margin: 36px 0 18px;
    color: #111827;
}

.code-box {
    background: #111827;
    color: #e5e7eb;

    padding: 24px;
    border-radius: 18px;

    font-size: 15px;
    line-height: 1.6;

    overflow-x: auto;
}

.code-box code {
    font-family: Consolas, Monaco, monospace;
}

@media (max-width: 768px) {
    .article-container {
        width: 94%;
        margin: 80px auto 35px;
    }

    .article-card {
        padding: 28px 18px;
    }

    .article-title {
        font-size: 30px;
    }

    .article-text {
        font-size: 16px;
    }

    .math-box {
        padding: 16px;
    }

    .back-button {
        top: 14px;
        left: 14px;
        padding: 10px 14px;
    }
}