Not just the way you combine them, but also the way you actually write them. This means if you are using a feature in CSS or HTML that's not supported in all browsers; What will happen to users that use a browser that does not support the feature you've implemented?
Based on the result, I categorize them into three categories namely; The Good, The Bad, and The Ugly.
Let's begin with the good.
Can you spot the difference? Don't worry its quite minimal.
For this page if any part of the web page fails to load it's considered bad.