Problem: The CSS specification is undergoing major changes. For example, CSS logical properties and values, CSS variables, etc. However, TemplateStyles has not kept up with the updated CSS specification. Therefore, when using these new properties and values, you will get the error "Unrecognized or unsupported property" and will not be able to save them.
Proposed solution: Update properties and values that are supported by all modern browsers (which can be found by checking Can I use) to correspond to TemplateStyles, unless experimental, deprecated, or cannot be supported for security reasons. If the CSS sanitizer requires significant effort to update to support all CSS, external tools (e.g., stylelint) may be utilized.
Who would benefit: Template authors who want to use new CSS properties. The same goes for Wikisource users who use Page styles.
