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

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Hiragino Sans GB", 
                 "Microsoft YaHei", "Helvetica Neue", Helvetica, Arial, sans-serif;
    line-height: 1.8;
    color: #333;
    background-color: #f5f7fa;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
}

header {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
    padding: 60px 0;
    text-align: center;
    box-shadow: 0 2px 10px rgba(0,0,0,0.1);
}

header h1 {
    font-size: 2.8em;
    margin-bottom: 10px;
    font-weight: 600;
}

header .subtitle {
    font-size: 1.2em;
    opacity: 0.95;
}

nav {
    background-color: white;
    box-shadow: 0 2px 5px rgba(0,0,0,0.08);
    position: sticky;
    top: 0;
    z-index: 100;
}

nav ul {
    list-style: none;
    display: flex;
    justify-content: center;
    flex-wrap: wrap;
}

nav ul li {
    margin: 0;
}

nav ul li a {
    display: block;
    padding: 15px 20px;
    color: #333;
    text-decoration: none;
    transition: all 0.3s;
    font-weight: 500;
    font-size: 0.95em;
}

nav ul li a:hover {
    background-color: #667eea;
    color: white;
}

main {
    padding: 40px 20px;
}

.section {
    background-color: white;
    margin-bottom: 30px;
    padding: 40px;
    border-radius: 10px;
    box-shadow: 0 2px 12px rgba(0,0,0,0.08);
}

.section h2 {
    color: #667eea;
    font-size: 2.2em;
    margin-bottom: 30px;
    padding-bottom: 15px;
    border-bottom: 3px solid #667eea;
}

.content {
    color: #555;
    font-size: 1em;
}

.content p {
    margin-bottom: 15px;
    line-height: 1.8;
}

.knowledge-card {
    background-color: #fafbfc;
    padding: 30px;
    border-radius: 8px;
    margin-bottom: 25px;
    border-left: 5px solid #764ba2;
    transition: all 0.3s;
}

.knowledge-card:hover {
    box-shadow: 0 4px 16px rgba(0,0,0,0.12);
    transform: translateY(-2px);
}

.knowledge-card h3 {
    color: #764ba2;
    font-size: 1.6em;
    margin-bottom: 20px;
    font-weight: 600;
}

.knowledge-content h4 {
    color: #667eea;
    font-size: 1.2em;
    margin-top: 20px;
    margin-bottom: 12px;
    font-weight: 600;
}

.knowledge-content h4:first-child {
    margin-top: 0;
}

.knowledge-content ul {
    margin-left: 20px;
    margin-bottom: 15px;
}

.knowledge-content ul li {
    margin-bottom: 8px;
    line-height: 1.7;
    color: #555;
}

.problem-solution {
    background-color: white;
    padding: 20px;
    border-radius: 6px;
    margin-top: 15px;
    margin-bottom: 15px;
    border: 1px solid #e1e4e8;
}

.problem-solution:last-child {
    margin-bottom: 0;
}

.problem-solution p {
    margin-bottom: 10px;
}

.problem-solution strong {
    color: #d73a49;
    font-weight: 600;
}

.problem-solution ul {
    margin-left: 20px;
    margin-top: 8px;
    margin-bottom: 8px;
}

.problem-solution ul li {
    margin-bottom: 6px;
    color: #666;
}

footer {
    background-color: #2c3e50;
    color: white;
    text-align: center;
    padding: 30px 0;
    margin-top: 40px;
}

footer p {
    margin: 5px 0;
    opacity: 0.9;
}

@media (max-width: 768px) {
    header h1 {
        font-size: 2em;
    }
    
    header .subtitle {
        font-size: 1em;
    }
    
    .section {
        padding: 25px 20px;
    }
    
    .section h2 {
        font-size: 1.8em;
    }
    
    nav ul {
        flex-direction: column;
    }
    
    nav ul li a {
        padding: 12px 20px;
        border-bottom: 1px solid #f0f0f0;
    }
    
    .knowledge-card {
        padding: 20px;
    }
    
    .knowledge-card h3 {
        font-size: 1.3em;
    }
}