editor.css

html,
body {
  height: 100%;
}

html {
  color-scheme: light dark;
}

body {
  display: grid;
  grid-template: 50% 50% / 100%;
  margin: 0;
}

button {
  cursor: pointer;
}

iframe {
  border: 0;
  order: 1;
  width: 100%;
  height: 100%;
}

nav {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
  position: absolute;
  inset-block-end: 1rem;
  inset-inline-end: 1rem;
}

nav > * {
  background: ButtonFace;
  border: 1px solid ButtonBorder;
  border-radius: 50%;
  color: ButtonText;
  padding: 0.5rem;
  display: grid;
  place-items: center;
}

nav > :hover,
nav > :focus {
  background: Canvas;
}

@media (min-width: 720px) {
  body {
    grid-template: 100% / 50% 50%;
  }
}