Build, test, and debug regular expressions
Matches a literal dot followed by either `css` or `scss` at the end of a line, typically used to detect CSS/SCSS file extensions in filenames, import statements, or file lists. The `g` flag finds all matches, while `m` makes `$` anchor to the end of each line rather than the whole string. Caveat: it does NOT exclude CSS module files—`styles.module.css` still matches because `.css` appears at the end; excluding those requires a negative lookahead such as `\.(?!module\.)(scss|css)$` or similar filename filtering.