content {
    width: 768px;
    margin: auto;
    height: 100%;
}

.clearfix:after
{
    content: "";
    display: block;
    clear: both;
}

box {
    height: 50px;
    float: left;
    margin-top: 20px;
}

.col {
    margin: 0 10px;
    height: 100%;
    box-sizing: border-box;
    background-color: #eee;
    border: 1px solid #999;
}

@media (min-width:768px) {
    .col-md-1 {
        width: 8.33%;
    }
    
    .col-md-2 {
        width: 16.66%;
    }
    
    .col-md-3 {
        width: 25%;
    }
    
    .col-md-4 {
        width: 33.33%;
    }
    
    .col-md-6 {
        width: 50%;
    }
    
    .col-md-8 {
        width: 66.66%:
    }
    .col-md-12 {
        width: 100%;
    }
    
}

@media(max-width:768px) {
    .col-sm-1 {
        width: 8.33%;
    }
    
    .col-sm-2 {
        width: 16.66%;
    }

    .col-sm-3 {
        width: 25%;
    }

    .col-sm-4 {
        width: 33.33%;
    }
    
    .col-sm-6 {
        width: 50%;
    }
    
    .col-sm-8 {
        width: 66.66%;
    }
    
    .col-sm-12 {
        width: 100%;
    }
}