If both digits are the same you could write just one, for example, #000000 for #000
<!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>background-color</title> <style rel='stylesheet' type='text/css'> body { background-color: yellow; } div#one { width: 50px; height: 50px; border: 1px solid rgb(128, 128, 128); margin: 5px; float: left; background-color: #000; } </style> </head> <body> <div id='one'></div> </body> </html>