Code: Select all
<!DOCTYPE HTML SYSTEM>
Code: Select all
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd">
The reason is that an invalid doctype will trigger "Quirks mode" in Opera, so it will try to "emulate" other browsers bugs. The complete description of how it works is decribed at Opera documentation.