Back end developers can make good looking web apps too – FullyBearded
fullybearded.com
fullybearded.com
There’s barely any research in this post.
Also, from experience, back-end folks often think of UI as fancy color scheme, but imho what they most often get wrong is proportion and spacing, so this is probably where I'd start to improve. For instance, read on visual hierarchy and white space.
But I've used FontAwesome before which I believe (or hope) is still the industry standard for free icons: https://fontawesome.com/ . Not sure if Heroicons or something else has displaced it in popularity rankings.
The other products -- Unsplash for photos, Undraw for illustrations -- were pretty cool references though and I'll be bookmarking them. Does anyone know if there are other resources for photos & illustrations that are popular among web developers?
The hard part is actually getting a good user experience. Which is just in part learning about and applying research done in this area, and on the other fighting off all the trash people want to shove into the app for engagement and growth.
Making it look good & not bloated still remains a challenge.