Datepicker Sizing

I've looked for the solution to this for sometime. I'm trying to resize the datepicker (mulitple months) UI interface and tried styling several elements in the CSS file i'm using. I see the size is always 420px no matter what theme I use, so I guess the sizing is handled within the JS? Can anyone tell me how I can alter the width and height of the datepicker??
Thanks for your help!