The core use case for layers is making it easier to combine multiple style sources into a single ... at least until the CSS Grid Layout module stepped into the breach. Grid is now fully supported ...

Now, the same Cascading Style Sheets (CSS) Working Group ... it builds on the CSS3 Box model module and adds functionality to flow the content of an element into multiple columns.

One of the more important details of understanding and using Cascading Style Sheets (CSS) is the cascading aspect of its name. That is, how are multiple rules for the same element handled?