body,html{
    width: 100%;
    height: 100%;
    margin: 0;
    padding: 0;
}
ul, li {
    list-style: none;
    padding: 0;
    margin: 0;
}
h2 {
    padding: 5px;
    margin: 0;
}
.button {
    margin: 10px;
}
#mask {
    position: absolute;
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.65);
    opacity: .75;
    display: none;
}
.box {
    width: 250px;
    height: 150px;
    background: #999;
    overflow: hidden;
    margin: 0 auto;
    margin-top: 200px;
}
#sources {
    width: 100%;
    height: 100%;
    background: #fff;
    overflow: auto;
}
.title {
    width: 100%;
    height: 20px;
    line-height: 20px;
    text-align: left;
    font-size: 14px;
    color: #fff;
}
.li {
    padding: 5px;
    cursor: pointer;
}
.li:hover {
    background: #eee;
}