* {
    margin: 0; padding: 0; border: 0; box-sizing: border-box; 
}

.boxes {
    width: 100%;
    margin: auto;
    
}

.box {
    float: left;
    border: 1px solid black;
    height: 300px;
    width: 33.33%;
    background-color: rgb(255, 255, 255);
    display: none;
}




@media only screen and (min-width: 0px) {
    .one {
        display: block;
    }
}


@media only screen and (min-width: 600px) {
    .two {
        display: block;
    }
}


@media only screen and (min-width: 1200px) {
    .three {
        display: block;
    }
}


@media only screen and (max-width: 1200px) {
    .two {
        width: 50%;
    }
}

@media only screen and (max-width: 1200px) {
    .one {
        width: 50%;
    }
}

@media only screen and (max-width: 600px) {
    .one {
        width: 100%;
    }
}