Sass (Syntactically Awesome Style Sheets) is an extension of CSS adding features like nested rules, variables, mixins and class extensions. This enables developers to write structured, manageable and reusable CSS. Sass is compiled into standard CSS.
- Stackoverflow.com Wiki
The @-Rules and directives in Sass are backbone features that you should at least know about, especially when it concerns the @import rule. Some of these @-rules are extensions of CSS @-rules while others are Sass specific directives. Either way it is best you know what these rules are for and how they work if you are going to be working with Sass.
Z-index is an inherently tricky thing, and maintaining z-index order in a complex layout is notoriously difficult. With different stacking orders and contexts, keeping track of them as their numbers increase can be hard — and once they start to spread across CSS files, forget about it! Because z-index can make or break a UI element’s visibility and usability, keeping your website’s UI in working order can be a delicate balance.
Embrace Sass once, and you may never want to go back to vanilla CSS again