body {
    padding: 0;
    margin: 0;
}

main {
    margin: -5px;
    
}

.item:nth-child(4n+1){clear:both}
.item:nth-child(2n){background-color:#5D6D7E}

.item {
    width: calc(25% - 10px); 
    box-sizing: border-box;
    float: left;
    border: 1px solid #2874A6;
    padding: 10px 0px;
    margin: 5px;
}