CSS: Add ::first-letter pseudo-element document

[ttstauss]

This is a basic introduction to the ::first-letter pseudo-element CSS selector. This document is meant to be a starting point and should be added to/expounded on.

P.S. I tried submitting a doc for the ::before selector, but apparently, it was already created, however, it's nowhere to be found in this directory (css/selectors/pseudo/). I wonder if a consolidation is in order 😛.

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[moT01]

This looks good @ttstauss, thanks for contributing to freeCodeCamp! I don't see a dedicated article on the before selector either - if you create one, it could probably be merged into the repo - In the future, could you please complete the checklist in the PR template (put an x by each item, assuming it's true - e.g. [x] I have read freeCodeCamp's contribution guidelines) - Thanks, and happy coding!