Simple Style Guide, Typography, Color & Shadow

Color Tone Terminology Handbook: Tint, Tone, Shade, and More

What is Color Theory?

What you must include in your brand's one-page style guide

Applying color to UI - Material Design

How to Create Beautiful Box Shadows in HTML and CSS

Style Guide Branding: Using Brand Colors, Fonts, and Logos

How to add a drop shadow in Photoshop - Adobe

Photoshop Layer Styles: Comprehensive Guide - WebFX

Unofficial style guide (WIP) available for those interested in

Creating Styleguides — the what, how and why behind it.

Styling with the CSS box-shadow property - LogRocket Blog

Simple Style Guide, Typography, Color & Shadow