This is a fairly simple way to add a thick underline to your elements.
We use here 2 interesting tricks:
- We Create a background gradient which both colors are positioned at the same point. This way there's no "gradient transition" at all, and the background seems like 2 different colors.
- Creating a <span> element inside the <H1> element (the span could be created inside any element). This way the background is kept relative to each line.