* {
    box-sizing: border-box;
}

html {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

header {
    text-align: center;
}

nav ul {
    list-style-type: none;
}

nav li {
    border: 1px solid black;
    padding: 0.5em;
    margin: 0 1em;
    text-align: center;
}

section {
    border: 1px solid black;
}