simple.css

/* Global variables. */
:root {
  /* Set sans-serif & mono fonts */
  --sans-font: -apple-system, BlinkMacSystemFont, "Avenir Next", Avenir,
    "Nimbus Sans L", Roboto, "Noto Sans", "Segoe UI", Arial, Helvetica,
    "Helvetica Neue", sans-serif;
  --mono-font: Consolas, Menlo, Monaco, "Andale Mono", "Ubuntu Mono", monospace;

  /* Default (light) theme */
  --bg: #fff;
  --accent-bg: #f5f7ff;
  --text: #212121;
  --text-light: #585858;
  --border: #d8dae1;
  --accent: #0d47a1;
  --code: #d81b60;
  --preformatted: #444;
  --marked: #ffdd33;
  --disabled: #efefef;
}

/* Dark theme */
@media (prefers-color-scheme: dark) {
  :root {
    color-scheme: dark;
    --bg: #212121;
    --accent-bg: #2b2b2b;
    --text: #dcdcdc;
    --text-light: #ababab;
    --border: #666;
    --accent: #ffb300;
    --code: #f06292;
    --preformatted: #ccc;
    --disabled: #111;
  }
  /* Add a bit of transparency so light media isn't so glaring in dark mode */
  img,
  video {
    opacity: 0.8;
  }
}

/* Reset box-sizing */
*, *::before, *::after {
  box-sizing: border-box;
}

/* Reset default appearance */
textarea,
select,
input,
progress {
  appearance: none;
  -webkit-appearance: none;
  -moz-appearance: none;
}

html {
  /* Set the font globally */
  font-family: var(--sans-font);
  scroll-behavior: smooth;
}

/* Make the body a nice central block */
body {
  color: var(--text);
  background: var(--bg);
  font-size: 1.15rem;
  line-height: 1.5;
  display: grid;
  grid-template-columns: 1fr 90% 1fr;
  margin: 0;
}
body > * {
  grid-column: 2;
}

/* Make the header bg full width, but the content inline with body */
body > header {
  background: var(--accent-bg);
  border-bottom: 1px solid var(--border);
  text-align: center;
  padding: 0 0.5rem 1rem 0.5rem;
  grid-column: 1 / -1;
}

body > header h1 {
  max-width: 1200px;
  margin: 1rem auto;
}

body > header p {
  max-width: 40rem;
  margin: 1rem auto;
}

/* Add a little padding to ensure spacing is correct between content and header > nav */
main {
  padding-top: 1.5rem;
}

body > footer {
  margin-top: 4rem;
  padding: 2rem 1rem 1.5rem 1rem;
  color: var(--text-light);
  font-size: 0.9rem;
  text-align: center;
  border-top: 1px solid var(--border);
}

/* Format headers */
h1 {
  font-size: 3rem;
}

h2 {
  font-size: 2.6rem;
  margin-top: 3rem;
}

h3 {
  font-size: 2rem;
  margin-top: 3rem;
}

h4 {
  font-size: 1.44rem;
}

h5 {
  font-size: 1.15rem;
}

h6 {
  font-size: 0.96rem;
}

/* Prevent long strings from overflowing container */
p, h1, h2, h3, h4, h5, h6 {
  overflow-wrap: break-word;
}

/* Fix line height when title wraps */
h1,
h2,
h3 {
  line-height: 1.1;
}

/* Reduce header size on mobile */
@media only screen and (max-width: 720px) {
  h1 {
    font-size: 2.5rem;
  }

  h2 {
    font-size: 2.1rem;
  }

  h3 {
    font-size: 1.75rem;
  }

  h4 {
    font-size: 1.25rem;
  }
}

/* Format links & buttons */
a,
a:visited {
  color: var(--accent);
}

a:hover {
  text-decoration: none;
}

/* Misc body elements */
hr {
  color: var(--border);
  border-top: 1px;
  margin: 1rem auto;
}

img,
video {
  max-width: 100%;
  height: auto;
  border-radius: 5px;
}