There are a lot of tool-kits and software that are purportedly very powerful, flexible, feature-packed etc. But most of them are rather difficult to setup, or have a steep learning curve, or lots of documentation to read,
... ... or ... ...
all of the above.
JQueryUI is the first tool-kit I've used that has instructions in a few succinct lines that I can easily understand, use, and just get it to work!
Highly recommend JQueryUI (and of course, JQuery) for all web GUI development work.