demo.css

body {
  font-family: system-ui;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

body.use-preferred-font {
  font-family: var(--preferred-font), system-ui;
}

#toolbar {
  position: sticky;
  width: 100%;
  top: 0;
  z-index: 100;
  overflow-y: auto;
}

#preferred-font {
}

#preferred-font::after {
  content: '(' var(--preferred-font) ')';
  display: inline;
}

main {
  max-width: 1024px;
}

main > .window-body {
  overflow: auto;
}

.example {
  margin: var(--margin) 0;
  padding-left: 16px;
}

details {
  margin-top: 8px;
}

details > summary {
  display: inline-block;
  cursor: normal;
  user-select: none;
  margin-bottom: 4px;
}

@media screen and (min-width: 750px) {
  section {
    display: flex;
    flex-direction: row;
  }

  section > *:first-child {
    flex: 0 0 200px;
  }

  section > div {
    flex-grow: 1;
  }
}

a {
  color: #00c;
  text-decoration: underline;
}