I'm looking for a light-weight UI toolkit written in Javascript (something like Swing) but I'd rather not use ExtJS because I fear that will slow things down tremendously. Are there any small UI toolkits out there that mainly focus on layouts?
The problems I face in particular are working with layouts. A lot of toolkits come with different layout styles (Floating, Grid, Split Panes) and that is quite hard with CSS (especially heights extending 100%). It's also to be used as a framework for other developers to easily create layouts and just apply their own CSS (for themes).