Difference between fixed, fluid, responsive layouts (#856)

Author: veronvynguyen

src/questions/css-questions.md

@@ -39,4 +39,5 @@ permalink: /questions/css-questions/index.html
 * Can you explain the difference between px, em and rem as they relate to font sizing?
 * Can you give an example of a pseudo class? Can you provide an example use case for a pseudo class? 
 * What is the difference between a block level element and an inline element. Can you provide examples of each type of element?
-* What is the difference between CSS Grid and Flexbox? When would you use one over the other?
+* What is the difference between CSS Grid and Flexbox? When would you use one over the other?
+* What's the difference between fixed, fluid and responsive layouts?