This is a Sass mixin to handle a 3-way dark mode. It relies on a data-theme attribute on your <html> element with a value of light or dark. If data-theme is absent (i.e. it's neither light nor dark), the system's preferred mode is used.
body {
// matches data-theme="light" or data-theme="auto" with system instructing light mode
@include light {
background: white;
color: black;