- Cascading Style Sheets, Level 1 - W3c recommendations.
-- https://www.w3.org/TR/REC-CSS1-961217.html - W3C: CSS Validation Service - Validate CSS documents by URL, text area, or upload.
-- https://jigsaw.w3.org/css-validator - W3C: Cascading Style Sheets - Features a guide and tutorials on using cascading style sheets.
-- https://www.w3.org/Style/CSS |