docs: clean up SCSS styles

[MeAkib]

Removes redundant or unused SCSS rules and improves formatting for better readability and maintainability.

[github-actions[bot]]

Deployed docs-preview for 7f409aeae5e4111cf1445beab8a69001bdf7a767 to: https://ng-dev-previews-comp--pr-angular-components-32168-docs-ray9fv6x.web.app

Note: As new commits are pushed to this pull request, this link is updated after the preview is rebuilt.

[adolgachev]

This looks good to me, including the slightly reduced top margin above the cards that you can see at https://ng-dev-previews-comp--pr-angular-components-32168-docs-ray9fv6x.web.app/cdk/categories but be good to get a 2nd internal opinion on this from @andrewseguin as well.