@media only screen and (min-width: 600px) {   
    main {
        display: grid;
        grid-template-columns: 1fr 1fr;

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

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

    }

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