style.css

html {
    scroll-behavior: smooth;
    margin-top: 2.5rem;
    padding-bottom: 20rem;
    font-size: 100%;
    overflow-y: scroll;
    -webkit-text-size-adjust: 100%;
    -ms-text-size-adjust: 100%;
}

@media (prefers-reduced-motion: reduced) {
    html {
        scroll-behavior: auto;
    }
}

:target {
    scroll-margin-top: 6.25rem;
    outline: 0.375rem solid mediumseagreen;
    animation: fadeOutOutline 1000ms 1000ms forwards;
}

@keyframes fadeOutOutline {
    to {
        outline-color: transparent;
    }
}

nav li li li {
    /* Hide subsubsections in the menu */
    display: none !important;
}

nav {
    display: inline-block;
    justify-content: center;
    text-align: center;
    margin: 0 auto;
}

nav ul {
    padding: 0;
    margin: 0.3125rem 3.125rem 1.25rem 5rem;
}

nav a {
    display: block;
    width: 6.25rem;
    padding: 0.625rem;
    background: #111;
    border-radius: 1.25rem;
    text-decoration: none;
}

nav li {
    list-style: none;
    position: relative;
    display: inline-block;
}

nav ul ul {
    padding: 0;
    margin: 0;
    position: absolute;
    display: none;
    z-index: 999;
}

nav li:hover ul {
    display: block;
}

nav li:hover>a {
    background-color: #222;
}

nav li:hover>a:hover {
    background-color: #333;
}

body {
    border-radius: 1.25rem;
    font-family: sans-serif, 'Noto Color Emoji', 'Apple Color Emoji', 'Segoe UI Emoji';
    font-size: 1rem;
    line-height: 1.7;
    padding: 0.125rem 1rem 0.5rem;
    margin: auto;
    max-width: 62.5rem;
    color: #ddd;
    background: black;
}

a {
    color: #3498db;
    text-decoration: none;
}

a:hover {
    color: lightblue;
}

a:focus {
    outline: thin dotted;
}

*::-moz-selection,
*::selection {
    background: rgba(255, 255, 0, 0.3);
}

p {
    margin: 1rem 0;
}

img {
    max-width: 100%;
}

h1,
h2,
h3,
h4,
h5,
h6 {
    line-height: 1;
    font-weight: normal;
}

h4,
h5,
h6 {
    font-weight: bold;
}

.title {
    font-size: 3.5rem;
    font-weight: bold;
    text-align: center;
}

h1.title::after,
h1::after {
    content: " ";
    display: block;
    margin-top: 0.75rem;
}

h1 {
    font-size: 2rem;
    font-weight: bold;
}

h1::after {
    border: 0.0625rem solid white;
}

h2 {
    font-size: 1.5rem;
}

h3 {
    font-size: 1.5rem;
}

h4 {
    font-size: 1.2rem;
}

h5 {
    font-size: 1rem;
}

h6 {
    font-size: 0.9rem;
}

blockquote {
    margin: 0;
    padding-left: 3rem;
    border-left: 0.5rem #EEE solid;
}

hr {
    display: block;
    height: 0.125rem;
    border: 0;
    border-top: 0.0625rem solid #aaa;
    border-bottom: 0.0625rem solid #eee;
    margin: 1rem 0;
    padding: 0;
}

pre,
code,
kbd,
samp {
    font-family: monospace, 'Noto Color Emoji', 'Apple Color Emoji', 'Segoe UI Emoji';
    font-size: 0.98rem;
}

pre {
    white-space: pre;
    white-space: pre-wrap;
    word-wrap: break-word;
}

b,
strong {
    font-weight: bold;
}

dfn {
    font-style: italic;
}

ins {
    background: #ff9;
    text-decoration: none;
}

mark {
    background: #ff0;
    font-style: italic;
    font-weight: bold;
}

sub,
sup {
    font-size: 0.75rem;
    line-height: 0;
    position: relative;
    vertical-align: baseline;
}

sup {
    top: -0.5rem;
}

sub {
    bottom: -0.25rem;
}

ul,
ol {
    margin: 1rem 0;
    padding: 0 0 0 2rem;
}

li p:last-child {
    margin-bottom: 0;
}

ul ul,
ol ol {
    margin: 0.3rem 0;
}

dl {
    padding: 0;
    margin: 0;
}

dd {
    font-size: 1rem;
}

dl dd:last-of-type {
    display: none;
}

dl:hover dd:last-of-type {
    display: block;
}

@media (max-width: 67.5rem) {
    .title {
        font-size: 2.5rem;
        text-align: center;
    }

    nav {
        background: #303030;
        font-size: 0.75rem;
        position: fixed;
        bottom: 0;
        left: 0;
        width: 100%;
        text-align: center;
    }

    nav ul {
        padding: 0.125rem;
        margin: 0.125rem auto;
    }

    nav a {
        width: 5rem;
        margin: 0.25rem;
        padding: 0.125rem;
        background: #111;
        border-radius: 1.25rem;
    }

    nav li:hover ul {
        display: none;
    }

    nav li:hover>a {
        background-color: #222;
    }

    nav li:hover>a:hover {
        background-color: #555;
    }

    h1.title::after {
        border: 0.0625rem solid white;
    }

    h1::after {
        border: none;
    }
}

@media (prefers-color-scheme: light) {
    body {
        background: white;
        color: black;
    }

    a,
    a:hover {
        color: blue;
        text-decoration: none;
    }

    nav a {
        background: lightgray;
    }

    nav li:hover>a,
    nav li:hover>a:hover {
        background-color: lightblue;
    }

    @media (max-width: 67.5rem) {
        nav {
            background: whitesmoke;
        }

        nav a {
            background: lightgray;
        }

        nav li:hover>a,
        nav li:hover>a:hover {
            background-color: lightblue;
        }

        h1.title::after {
            border: 0.0625rem solid black;
        }

        h1::after {
            border: none;
        }
    }
}