@media (min-width: 500px) {
    main {
        grid-template-columns: 1fr 1fr;   
    }
    
    .div1 {
        grid-column: 1/2;
        grid-row: 1;
    }
    
    .div2 {
        grid-column: 2/3;
        grid-row: 1;
    }
    
    .div3 {
        grid-column: 1/2;
        grid-row: 2;
    }
}