#banner {
text-align: center;
}
#banner> a {
display: inline-block;
    width: calc(31.999% - 25px);
    float: none;
}
#banner> a:nth-child(4n+1) {
    margin-left: 30px;
    clear: inherit;
}

@media screen and (max-width: 900px) {
#banner {
    width: calc(100% - 12px);
    padding-right: 20px;
}

#banner a {
    width: calc(49% - 15px);
    margin: 0 0 15px 15px;
}

#banner a:nth-child(2n) {
    float: none;
}

#banner> a:nth-child(4n+1) {
    clear: inherit;
    margin-left: 12px;
}
#banner a:nth-child(2n+1) {
    float: none;
}
}