Originally in www_lsst_io we tried to used styled-theming to build a design system, including a dark mode. The problem, though, is that these styles aren't getting added to the site on initial load (they do after an in-app page transition, though). I think that a safer and more compatible approach will be to take out the styled-theming integration and instead build up a design system using CSS custom properties. This will also let us support a dark mode (https://github.com/insin/gatsby-plugin-dark-mode)