@media only screen and (min-width: 1200px) {   
        main{
        grid-template-columns: 1fr 1fr 1fr;
    }

    .section1 {
        grid-column:1/2 ;
        grid-row:1/2;
    }

    .section2 {
        grid-column:2/3 ;
        grid-row:1/2;

    }

    .section3 {
        grid-column:3/4 ;
        grid-row:1/2;
    }
}