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.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.