style.css

/********************
    =GENERAL
********************/

body {
    margin: 0;
    font-family: "Montserrat", "Avenir";
    background-color: #232323;
}

h1 {
    margin: 0;
}

nav ul li button, h1 {
    text-transform: uppercase;
}

/********************
    =HEADER
********************/

header {
    background-color: #4482B6;
    color: #fff;
}

header h1 {
    margin: 0;
    padding-bottom: 1em;
    text-align: center;
    font-weight: normal;
}

#colorDisplay {
    font-size: 2em;
}

#colorDisplay::after,
#colorDisplay:before {
    content: '\A';
    white-space: pre-wrap;
}

/********************
    =NAVIGATION
*********************/

#message {
    color: #000;
}

nav {
    background: #fff;
}

nav > ul {
    list-style: none;
    margin: 0 0 1.5em 0;
    padding: 0;
    white-space: nowrap;
    text-align: center;
}

nav > ul li {
    display: inline-block;
}

nav > ul li button {
    padding: 0.5em 0.5em;
}

nav li:not(#message):hover {
    background-color: #4482B6;
}

nav li:hover button {
    color: #fff;
}

nav li button {
    padding: 0;
    margin: 0;
    border: 0;
    background: 0;
    color: #4482B6;
    font-weight: 700;
    font-size: inherit;
    letter-spacing: 1px;
}

.left {
    margin-right: 7em;
}

.selected {
    background-color: #4482B6;
    color: #fff;
}

/********************
    =CONTAINER
*********************/

.container {
    max-width: 600px;
    margin: 0 auto;
    text-align: center;
    font-size: 0;
}

.square {
    width: 30%;
    padding-bottom: 30%;
    margin: 1.66%;
    border-radius: 10%;
    display: inline-block;
    font-size: 1rem;
}