How to make Horizontal Lines with CSS only

Recently we came across a situation, where we had to add new custom donation forms to a page. The plugin required that we update the functions.php file of the WordPress Theme. Having no access to the actual HTML (without building a new WordPress Theme Template), we still needed a way to create a horizontal line in between the regular form section, and our new custom donation questions. We found an easy way using CSS. Learn how to create a horizontal element across the page, using only CSS.