A short guide about building dark/light mode (theme) comprising prefers-color-scheme property and the ability for the user to manually override. Properly structured HTML, CSS custom properties in respective scope, two radio buttons, SVG icons, and general sibling combinator will do the job! This is CSS-only approach.

HTML entity list based on W3C sources from 15.02.2022. Includes expressions, decimal and hexadecimal codes, and descriptions. If a font does not provide used characters or icons, Mozilla Firefox and Google Chrome replace them with the system font. Using HTML entities is safe and recommended. The ... character indicates additional character entities. On hover, more details is displayed.