{# `data-base` is what makes a custom theme inherit: tokens.css matches `[data-base="shire"]` as well as `[data-theme="shire"]`, so a custom light theme gets the whole parchment palette underneath its own handful of colours. Without it, four light colours would sit on Moria's near-black surfaces. `data-themes` is the list of `id:base` pairs, which is what the browser needs in order to set both attributes when somebody switches -- one attribute to split rather than a JSON island to parse. #}