• CSS Modules & Working Groups: https://www.w3.org/TR/tr-groups-all#tr_Cascading_Style_Sheets__CSS__Working_Group
• CSS Variables: https://developer.mozilla.org/en-US/docs/Web/CSS/Using_CSS_variables
• Vendor Prefixes: https://developer.mozilla.org/en-US/docs/Glossary/Vendor_Prefix
• Which Vendor Prefixes should you use? => http://shouldiprefix.com/
• @supports: https://developer.mozilla.org/en-US/docs/Web/CSS/%40supports
• BEM in Detail: http://getbem.com/introduction/
• An introduction to Bootstrap 4: https://academind.com/learn/css/bootstrap-4-tutorial/