* {
    box-sizing: border-box;
}

body {
    background: lightcoral;
}

img {
    max-width: 100%;
}

.container {
    max-width: 1100px;
    margin: 0 auto;
}

header, .left, .center, .right, footer {
    border: 1px solid;
    padding: 20px;
}

header, footer {
    text-align: center;
}

header {
    margin-bottom: 10px;
}

footer {
    margin-top: 10px;
}

main {
    display: flex;
    gap: 10px;
}

.left, .right {
    width: 25%;

}

.center {
    width: 50%;
}

/* max-width = desktop-first */
/* min-width = mobile-first */

/* tablet */
@media screen and (max-width: 900px) {
    body {
        background: rgb(0, 255, 255);
    }

    main {
        flex-wrap: wrap;
    }

    .left {
        width: 100%;
    }

    .center, .right {
        width: calc(50% - 5px);
    }
}

/* phone */
@media screen and (max-width: 600px) {
    body{
        background: rgb(116, 194, 150);
    }

    .center, .right {
        width: 100%;
    }
}