zgohr/feather — comment on commit cb8206e130194e74ca2de7657a784bc5f36141c4
File: blog/public/widgets/header/header.css line 1
By ryedin:

never target CSS rules by ids, always use classnames. This is just Good Practice in general, but the main reason for this is that IDs are brittle (refactoring the widget hierarchy later can cause the autogenerated IDs to be different, rendering your CSS broken).

All widgets are automatically embedded into a container div whose class name will be in the form "namespace_widgetName"... hence our classname based ruled that you removed from this file ".blog_header".