body
{background-color: saddlebrown;

}
aside, box1, box2, box3 {display:block;
}
aside{
    background-color:yellow;
    width:90%;
    height: 400px;
    margin: 0;
    padding-left: 10%;
    padding-right:10%;
    z-index: 1;
}

article1{
    background-color: red;
    width: 25%;
    height: 300px;
    float: left;
    margin: 3%;
    
    font-family:Arial, Helvetica, sans-serif;
}

article2{
    background-color: blue;
    width: 25%;
    height: 300px;
    float: left;
    margin:3%;
}

article3{
    background-color: green;
    width: 25%;
    height: 300px;
    float: left;
    margin: 3%;