The border-width property can take either one of three keywords or a length value.
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html xmlns='http://www.w3.org/1999/xhtml' xml:lang='en'> <head> <title>border</title> <style rel='stylesheet' type='text/css'> div#border-width { overflow: hidden; } div#border-width div { float: left; border-style: solid; border-color: red; margin: 0 5px; } div#thin { border-width: thin; } div#medium { border-width: medium; } div#thick { border-width: thick; } </style> </head> <body> <div id='border-width'> <div id='thin'>thin</div> <div id='medium'>medium</div> <div id='thick'>thick</div> </div> </body> </html>