body {
    font-family: 'Gill Sans', 'Gill Sans MT', Calibri, 'Trebuchet MS', sans-serif;
}

main {
    .red {
        display: inline-block;
        text-align: center;
        background-color: red;
        height: 100px;
        width: 100px;
        outline: 5px solid black;
        font-size: 70px;
        margin: 20px;
    }

    .green {
        display: inline-block;
        text-align: center;
        background-color: green;
        height: 100px;
        width: 100px;
        outline: 5px solid black;
        font-size: 70px;
        margin: 20px;
    }

    .blue {
        display: inline-block;
        text-align: center;
        background-color: blue;
        height: 100px;
        width: 100px;
        outline: 5px solid black;
        font-size: 70px;
        margin: 20px;
    }
}

header {
    font-size: 50px;
    text-align: center;
    font-weight: bold;
}


.container {
    width: 1400px;
    margin: 0 auto;
    display: flex;
    background-color: yellow;
    outline: 1px solid black;
    flex-direction: column;
    justify-content: center;

    main {
        display: flex;
        flex-wrap: wrap;
    }
}

.footer {
    background-color: gray;
    text-align: center;
    border: 1px solid black;
}

.footer span {
    font-size: 50px;
    margin-left: 10px;
    margin-right: 10px;
}

#date {
    font-size: 20px;
    font-weight: normal;
}

@media(max-width: 1400px) {
    body {
        background-color: gray;
    }

    .container {
        width: 840px;
    }
}

@media(max-width: 840px) {
    body {
        background-color: lightblue;
    }

    .container {
        max-width: 560px;
    }
}

@media(max-width: 600px) {
    .container {
        width: 150px;
    }

    header {
        font-size: 20px;
    }

    body {
        background-color: orange;
    }

    .footer span {
        font-size: 30px;
        margin-left: 10px;
        margin-right: 10px;
    }

    #date {
        font-size: 15px;
        font-weight: normal;
    }
}