Get a feel for it; on the sidebar you'll see "main-style.css" as well as an HTML page for every page on your website. Select "main-style.css" to view the stylesheet in Weebly's editor.

Your template file may have a different name, so use the correct name in place of "template.css." Your HTML head section looks similar to this example: Save the HTML file.

All you have to do is visit Paste HTML, enter some code, publish it, and look at what you made. Paste HTML supports HTML, CSS, and JavaScript. You can even use Markdown if you want.