style.css

body {
    background: #ccc;
    font-family: Helvetica, Arial, sans-serif;
    font-size: 20px;
}

* {
    box-sizing: border-box;
}

#container {
    width: 720px;
    margin: 3em auto;
}

/*** header ***/

header {
    background: #fff;
    max-width: 320px;
    padding: 8px 16px;
}

#logo {
    font-weight: bold;
    font-size: 48px;
}

/*** main nav ***/

ul.nav {
    background: #fff;
    margin-top: 60px;
    font-size: 1.5em;
    height: 60px;
    display: flex;
    justify-content: space-around;
    align-items: center; 
    width: 100%;
}

.nav li a {
    text-decoration: none;
}

/*** main section ***/

main {
    background: #fff;
    padding: 32px 32px;
    margin-top: 3em;
}

/*** some basic elements ***/

h2 {
    font-size: lem;
    font-weight: bold;
}

a, a:visited, a:hover, a:active {
    color: hotpink;
}

p {
    margin-top: 2em;
}

code {
    color: blue;
    font-family: monospace;
    background: lightblue;
}

/*** forms ***/

form {
    margin: 1em 0;
    border: #cdcdcd 1px solid;
    padding: 1em;
}

form label {
    display: block;
    color: #555;
    margin-top: 1.5em;
    font-weight: bold;
    font-size: 0.75em;
}

form label:first-child {
    margin-top: 0;
}

form input[type=text] {
    margin-top: 0.25em;
    display: block;
    min-width: 50%;
    font-size: 1em;
    padding: 0.25em 0.5em;
}

form button {
    margin-top: 1.5em;
    padding: 0.5em 2em;
    font-size: 1em;
    font-weight: bold;
    cursor: pointer;
}