ul{
    margin: 0;
    padding: 0;
}
li{
    list-style: none;
}
.main-container{
    width: 1200px;
    margin: 0 auto;
    background: url('./../img/topics-banner.png') no-repeat #fff;
    padding: 200px 0 50px;
}

.main-container ul{
    width:950px;
    margin: 0 auto;
    padding: 50px 100px;
    background:rgba(255,255,255,1);
    box-shadow:0px 6px 23px 1px rgba(213,212,212,0.3);
    box-sizing: border-box;
}
.main-container ul li{
    display: block;
    margin-bottom: 20px;
}