Add CSS for in-page styles
Description
- Introduces CSS for applying in-page styles according to each doc
- Allow us to deprecate the feature pages on the about website without losing all visual elements
- Allow us to improve the layout/design on specific docs
woot woot woot
More styles to be added on the go :)
Before and after screenshots
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Related issues and links
- Needed for https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/21798
- Helpful for &305 (closed)
cc/ @gl-docsteam