* {
    margin: 0;
    padding: 0;
}

body {
    color: white;
    font-family: sans-serif;
    text-align: center;
    margin: 40px;
}

/* large */

@media only screen and (min-width: 768px) {
    body {
        background-color: blue;
        font-size: 2em;
    }
    h1 {
        font-size: 2.5em;
        margin-bottom: 0.5em;
    }

    #medium,
    #small {
        display: none;
    }

    .col1, .col2, .col3 {
        display: inline-block;
    }
}

/* medium*/

@media only screen and (max-width: 768px) and (min-width: 301px) {
    body {
        background-color: green;
        font-size: 1.5em;
    }
    h1 {
        font-size: 2.5em;
        margin-bottom: 0.5em;
    }

    p {
        margin-bottom: 1em;
    }

    #large,
    #small{
        display: none;
    }

    .col1 {
        float: left;
        margin: 0;
        width: 66.66%;
    }
    .col2 {
        float: left;
        margin: 0;
        width: 33.33%
    }
    .col3 {
        width: 100%;
    }
}

/* small */

@media only screen and (max-width: 300px) {
    body {
        background-color: red;
        font-size: 1em;
    }

    h1 {
        font-size: 3em;
        margin-bottom: 0.5em;
    }

    #large,
    #medium {
        display: none;
    }

    .col1, .col2, .col3 {
        display: block;
        margin-bottom: 1em;
    }
}