Theme Stylesheet and Functions file

Stylesheet

One of the most important files in any WordPress theme is its stylesheet. Without the stylesheet, one cannot activate a WordPress theme properly. It will either result in a broken theme or you may face the missing stylesheet error.

You are also required to have a style.css file to add important information about your theme, like its name, author name, and description (metadata). Here’s what it looks like  – Theme File Header Example.

Functions

The functions.php file plays another major role in WordPress theme development. It is mainly used for enabling specific features like sidebars, post formats, and custom headers on a WordPress site. You can learn more about it from the below video.

Tabby Chapman: Functions.php And How To Quit It from WordPress.tv | (CC BY-SA 4.0)