As you go about designing and coding your application's screens, here are a few things that you may find useful.

Readings

I've placed them in rough order of my opinion of their value/length ratio.

• ​Butterick's Typography In Ten Minutes​

• ​Web Design in 4 minutes​

• ​7 Rules for Creating Gorgeous UI - and part 2​

• ​Google's Material design guidelines​

Resources

In rough order of how often I use them.

• ​Official Bootstrap Documentation​

• ​Font Awesome - Free, CSS-customizable, perfectly scalable icons for almost everything.

• ​Bootswatch - Cheating. Great for quick styles while prototyping.

• ​Google Web Fonts - You'll want this after reading Butterick's.

• ​Stock Up - A search engine for free stock photos.

• ​Shoelace.io - A tool to help you create your Bootstrap grid layout.

• ​Beautiful Web Type and Typographic Project - A curated showcase of Google Web Fonts.

• ​HTML5 Element List - An excellent, categorized list of HTML elements.

• ​Bootstrap CDN - Instantaneous <link>ing to Bootstrap or Bootswatches.

• ​Firefox Tilt3D Extension - A tool to help you visualize what's going wrong with your layout.

• ​CSS3 Generator - Generate CSS box shadows, text shadows, and gradients.

• ​Subtle Patterns - A library of free, tileable, subtle background images.

• ​Adobe Color - Generate complementary colors.