How do I create div element programmatically with a certain height and background transparency starting from 0 to 100% all over its height?

Answer 1

From what I am understanding, you'd like to have a gradient that fades to transparency as a background.

CSS:

.divclassname{ background-image: linear-gradient(to right, rgba(255,0,0,0), rgba(255,0,0,1));}

Use the linear-gradient declaration with the background-image property with RGBA as your color system.