I've got to recommend refactoringui.com. They sell a (rather expensive) book on web/mobile app design that explains how to build your design system and use it to create great looking apps. They cover all the bases you would expect like fonts, line-heights, colors, shadows, borders, sizing, working with images, visual hierarchy, using white space, etc. etc. I'm a developer by trade and I work primarily with one other…
I don't know. Just looking at one of the things that they've posted: https://twitter.com/steveschoger/status/981606881255976961 > Overlapping images is a great way to add depth to an interface and make it look more “designed”. I don't know if this is sarcasm. No one is asking why do we need to add "depth"? What problem is "depth" of overlapping icons solving? I would stay away from this.
Anyone who can draw knows what that means.