How to Put Black Line in CSS. The HR tag enables you to include a gray horizontal rule in your Web page that is useful for dividing sections of data to keep things organized or for aesthetic ...

Margin distances are measured in percentages, pixels, points, centimeters and ems. You can add margins to content boxes by inserting an in-line CSS style.

Master CSS headers with this complete guide. Styling, hierarchy, and branding tips for better websites. Updated for 2025.