The default value is visible, which allows overflowing content to be rendered outside the containing block.
<!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"> <head> <title></title> <style type="text/css"> * .ex1 { width: 100px; height: 30px; background: yellow; } </style> </head> <body> <div class="ex1"> this is a test. this is a test. this is a test. this is a test. this is a test. this is a test. this is a test. this is a test. </div> </body> </html>