body{
    background-color: gainsboro;
    margin: 0px ;
}
.main{
    width: 400px;
    height: 400px;
    margin: 0px auto;
}
.k{
width: 200px;
height: 200px;
float: left;

}
.kutu-1{
    background-color: aqua;
}
.kutu-2{
    background-color: fuchsia;
}
.kutu-3{
    width: 400px;
    height: 200px;
    background-color: green;
    clear: left;
    clear: both;
}