*{
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    border: 1px solid red;
}

body{
    font-family: arial;
}


/* Extra small devices (phones, 600px and down) */
@media only screen and (max-width: 600px) {
    .container{
        display: flex;
        flex-direction: column;
    }
    
    .container div{
        height: 200px;
    }
}

/* Small devices (portrait tablets and large phones, 600px and up) */
@media only screen and (min-width: 600px) {
  .container{
        display: flex;
        flex-direction: row;
        flex-wrap: wrap
    }
    
    .container div{
        width: 50%;
        height: 200px;
    }
}

/* Medium devices (landscape tablets, 768px and up) */
@media only screen and (min-width: 768px) {
    .container{
        display: grid;
        grid-template-columns: repeat(12, auto);
        grid-template-rows: auto auto auto auto;
    }
    
    .container div{
        width: 100%;
    }
    
    .item1{
        grid-column: 1/13;
        grid-row: 1/3;
        height: 200px;
    }
    
    .item2, .item3, .item4, .item5, .item6{
        height: 100px;
    }
    
    .item2, .item3, .item4{
        grid-row:3/4;
    }
    
    .item2{
        grid-column:1/5;
    }
    
    .item3{
        grid-column:5/9;
    }
    
    .item4{
        grid-column:9/13;
    }
    
    .item5, .item6{
        grid-row: 4/5;
    }
    
    .item5{
        grid-column: 1/10;
    }
    
    .item6{
        grid-column: 10/13;
    }

}

/* Large devices (laptops/desktops, 992px and up) */
@media only screen and (min-width: 992px) {
    
}

/* Extra large devices (large laptops and desktops, 1200px and up) */
@media only screen and (min-width: 1200px) {
    
}