css query all div or code example

Example 1: what is a css selector

h1 {
  color: red;
}

In this CSS code example that sets the color of all h1s to red 
the "h1" is the selctor because we are applying this style to 
the h1s.

Example 2: how to use child selectors in css

ul li { margin: 0 0 5px 0; }
ul > li { margin: 0 0 5px 0; }