Change font-size after load

Hey,

I found a posibility for to change "height" after load the CKEditor

CKEDITOR.instances.key30.resize('100%', height);

Now want to do the same with "contentsCss" like this:

CKEDITOR.config.key30.contentsCss: 'body { font-size: 12; }'

..but of course this is wrong

Is that posible ?

Thanke for your help!!

Greetings Martin°^°