/* 网站背景图 - 渐变效果 */
.ad-background {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: -1;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
}

/* 备选渐变方案 */
.ad-background-blue {
    background: linear-gradient(135deg, #1a2980 0%, #26d0ce 100%);
}

.ad-background-purple {
    background: linear-gradient(135deg, #8e2de2 0%, #4a00e0 100%);
}

.ad-background-sunset {
    background: linear-gradient(135deg, #ff512f 0%, #dd2476 100%);
}

.ad-background-ocean {
    background: linear-gradient(135deg, #2193b5 0%, #6dd5ed 100%);
}

.ad-background-deepblue {
    background: linear-gradient(135deg, #0f0c29 0%, #302b63 50%, #24243e 100%);
}