Theme with variable width inside settings

[Heddson]

In the CSS you can use something like this
#{$header_width} .

Check this topic:

Add settings to your Discourse theme

Discourse has the ability for themes to have “settings” that can be added by theme developers to allow site owners to customize themes through UI without having to change any line of code and worry about losing their changes with future updates for the theme. Adding settings to your theme Adding settings to your theme is a bit different from adding CSS and JS code, that is there is no way to do it via the UI. The way to add settings is to create a repository for your theme, …