Under Windows WebDialogs will not use proper standard render mode because the IE engine is more conservative with embedded web controls. A `<meta>` tag is needed: `<meta http-equiv="X-UA-Compatible" content="IE=edge"/>` This should be at the very top of the `<head>` even before character encoding declaration and will ensure it will use the latest IE mode.

https://github.com/thomthom/sketchup-webdialogs-the-lost-manual/wiki/Doctype---Quirks-vs-Standard-vs-Superstandard