.sign {
    height: 100%;
    text-align: center;
    font-size: 1rem; /* 替换14px为相对单位 */
    font-family: "Microsoft YaHei", "微软雅黑", "Helvetica Neue", Helvetica, "PingFang SC", Tahoma, Arial, sans-serif;
    background-color: #f1f1f1;
    background: url(../img/login/login_bg.jpg) no-repeat center fixed;
	background-size: cover;
    overflow: hidden;
}
.logo {
    position: absolute;
    top: 56px;
    margin-left: 50px;
}
.main {
    width: 360px;
    margin: 20px 0 0 0;
    padding: 20px 30px 0 30px;
    background-color: #fff;
    border-radius: 4px;
    box-shadow: 0 0 8px rgba(0,0,0,.1);
    vertical-align: middle;
    display: inline-block;
}

@media screen and (max-width: 768px){
    .main {
        width: 80%;
        max-width: 312px;
        margin: 20px auto;
        border-radius: 8px;
    }
    .sign {
        padding: 20px;
        font-size: 0.9rem; /* 移动端稍小字体 */
    }
}

/* 高分辨率设备字体增强 */
@media (min-width: 1920px) {
    .sign {
        font-size: 1.125rem; /* 高分辨率设备增大字体 */
    }
}