Surprised nobody here has mentioned Google Web Toolkit yet. It's the tool Google uses to build interfaces like Gmail and (I believe) Docs. Freely available: https://developers.google.com/web-toolkit/
That said, it's not something I would want to use myself (not a Java fan).
It's also worth noting that Gmail especially appears to rely very heavily on Javascript for positioning and styling, rather than pure CSS. Many elements have, eg; `style="width: 123px"`. This is a practice I strive to avoid, so it's interesting to me that Google makes such use of it.
It's also worth noting that Gmail especially appears to rely very heavily on Javascript for positioning and styling, rather than pure CSS. Many elements have, eg; `style="width: 123px"`. This is a practice I strive to avoid, so it's interesting to me that Google makes such use of it.