switching/main.css

body {
    font-family: sans-serif;
    margin: 0;
}

.mainContainer {
    width: 1024px;
    margin: auto;
}

.mainContainer > h1 {
    text-align: center;
}

nav {
    display: flex;
    overflow: hidden;
    background-color: #93ff83;
}

nav > a {
    flex: auto;
    display: block;
    float: left;
    padding: 20px;
    box-sizing: border-box;
    text-decoration: none;
    font-weight: bold;
    color: inherit;
    text-align: center;
}

nav > a:visited {
    color: inherit;
}

.thumbnails {
    text-align: center;
    overflow: hidden;
}

.thumbnails > a {
    display: block;
    box-sizing: border-box;
    float: left;
    width: 25%;
    height: 200px;
    padding: 5px;
}

.thumbnails > a > div {
    box-sizing: border-box;
    height: 100%;
    border-radius: 5px;
    font-size: 24px;
    padding-top: 20px;
}

.c1 {
    color: aliceblue;
    background-color: darkred;
}

.c2 {
    color: aliceblue;
    background-color: midnightblue;
}

.c3 {
    color: aliceblue;
    background-color: indigo;
}

.c4 {
    color: aliceblue;
    background-color: seagreen;
}