| <!DOCTYPE html> |
| <!-- |
| | If both "margin-left" and "margin-right" are "auto", their used values |
| | are equal. This horizontally centers the element with respect to the edges |
| | of the containing block. |
| | https://www.w3.org/TR/CSS21/visudet.html#blockwidth |
| --> |
| <html> |
| <head> |
| <style> |
| .containing-block { |
| background-color: #2196f3; |
| padding: 10px 0; |
| margin-bottom: 10px; |
| width: 500px; |
| } |
| .block { |
| /* TODO: Add borders when supported. */ |
| background-color: #3f51b5; |
| display: block; |
| height: 5px; |
| margin: 0 auto; |
| padding: 0 100px; |
| width: 100px; |
| } |
| </style> |
| </head> |
| <body> |
| <div class="containing-block"> |
| <div class="block"></div> |
| </div> |
| </body> |
| </html> |
