* { box-sizing: border-box; }
body {
    margin: 0;
    font-family: "Segoe UI", "Microsoft YaHei", sans-serif;
    background: #f9fafc;
    color: #333;
}
.demo-header {
    text-align: center;
    padding: 60px 20px 40px;
}
.demo-header h1 {
    font-size: 38px;
    color: #222;
    margin-bottom: 16px;
}
.demo-header p {
    font-size: 18px;
    color: #555;
    max-width: 700px;
    margin: 0 auto;
    line-height: 1.8;
}

.section {
    display: flex;
    align-items: center;
    justify-content: space-between;
    max-width: 1100px;
    margin: 80px auto;
    padding: 40px;
    background: #fff;
    border-radius: 16px;
    box-shadow: 0 4px 16px rgba(0,0,0,0.05);
    flex-wrap: wrap;
}

.section img.preview {
    width: 48%;
    border-radius: 12px;
    box-shadow: 0 0 10px rgba(0,0,0,0.08);
}

.section .info {
    width: 48%;
}

.section h2 {
    font-size: 28px;
    margin-bottom: 16px;
    color: #0078ff;
}

.section p {
    font-size: 16px;
    line-height: 1.8;
    margin-bottom: 24px;
    color: #555;
}

.btn {
    display: inline-block;
    padding: 12px 28px;
    border-radius: 6px;
    background: #0078ff;
    color: #fff;
    text-decoration: none;
    font-size: 16px;
    transition: 0.3s;
}
.btn:hover {
    background: #005fd1;
}

.qr {
    width: 140px;
    height: 140px;
    border: 1px solid #ddd;
    border-radius: 8px;
}

@media (max-width: 900px) {
    .section {
        flex-direction: column;
        text-align: center;
        padding: 20px;
    }
    .section img.preview,
    .section .info {
        width: 100%;
    }
    .section img.preview {
        margin-bottom: 20px;
    }
}