Contains a selector, that is, adding spaces, which is used to select descendant elements under the specified label element. For example, the code in the code editor on the right:

.first span{color:red;}

This line of code will make the "cowardly" in the first paragraph of text "Rat" font color changes to red.

Please note the difference between this selector and a child selector. A child selector only refers to its direct descendants, or you can understand it as the first generation descendants that act on child elements. The descendant selector acts on all child descendant elements. Descendant selectors select with spaces, while child selectors select with ">".

Summary: > Acts on the first generation descendants of the element, and spaces act on all descendants of the element.