Thank you!
It's all about practice, you can make a simple gradient by making 3 lines, the first line has around 40% transparency and goes first, then the second line has around 60% transparency... the last line has 100% transparency.
I usually have a base color [ the darker blue you saw up there, then you get a lighter color based on the darker one ]
About proportions, yep... i have been drawing for more than a decade so... there's a lot of practice involved.