How to Put Black Line in CSS. ... Cascading style sheets, or CSS, enable you to define display and layout rules for HTML content, such as data blocks, borders and colors.

The preferred practice is to put style information in a separate file with a .css extension. Using formatting information contained within an external cascading style sheet is accomplished via the ...

It uses a click-and-drag interface for adding content to any page. If you have some CSS know-how or want to look at the source code for your website, Weebly offers an Advanced Editor for CSS and HTML.