This article covers the general styling used across the site. Specific template or element styling may be covered in their own posts. All Custom CSS is in the Customizer > Additional CSS.
Theme Elements
Navigation underline
Add shadow border to navigation to match sticky navigation.
.main-navigation { box-shadow: 0 2px 2px -2px rgba(0, 0, 0, .2); }
Navigation Search
Add background color to Navigation Search
.navigation-search { background-color: #fafafa; }