/* ===== 全局重置 ===== */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: system-ui, sans-serif;
}

html, body {
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

/* ===== 顶部导航栏 ===== */
header {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    background: #ffffff;
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.08);
    z-index: 100;
}

nav {
    max-width: 1200px;
    margin: 0 auto;
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 12px 24px;
}

.logo img {
    object-fit: contain;
    display: block;
}

.nav-links {
    display: flex;
    gap: 32px;
}

.nav-links a {
    text-decoration: none;
    color: #222;
    font-size: 16px;
    transition: color 0.2s;
}

.nav-links a:hover {
    color: #4080ff;
}

.nav-links a.nav-active {
    color: #4080ff;
    font-weight: 600;
}

/* ===== 主体内容 ===== */
main {
    flex: 1;
    background: linear-gradient(135deg, #edf4f9, #e8f0f8);
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    padding-top: 80px;
    padding-bottom: 40px;
}

.card {
    background: #fff;
    padding: 40px 50px;
    border-radius: 16px;
    box-shadow: 0 8px 24px rgba(0, 0, 0, 0.1);
    max-width: 520px;
    width: 92%;
}

.card h1 {
    text-align: center;
    color: #222;
    margin-bottom: 20px;
    font-size: 1.7rem;
}

.card .intro {
    text-align: center;
    font-size: 18px;
    color: #333;
    margin-bottom: 16px;
}

.card p {
    line-height: 1.8;
    color: #333;
}

.card ul {
    padding-left: 22px;
    line-height: 2;
    font-size: 16px;
}

.card .back-link {
    display: inline-block;
    margin-bottom: 16px;
    color: #4080ff;
    text-decoration: none;
}

.card .back-link:hover {
    text-decoration: underline;
}

/* ===== 页脚 ===== */
footer.site-footer {
    text-align: center;
    color: #666;
    font-size: 14px;
    padding: 24px 12px;
}

footer.site-footer p {
    margin: 4px 0;
}

footer.site-footer a {
    color: #4080ff;
    text-decoration: none;
}

footer.site-footer a:hover {
    text-decoration: underline;
}

/* ===== 移动端适配 ===== */
@media (max-width: 520px) {
    .nav-links {
        gap: 14px;
    }
    .nav-links a {
        font-size: 14px;
    }
    .card {
        padding: 28px 24px;
    }
}