How to define multiple CSS attributes in jQuery?

Better to just use .addClass() and .removeClass() even if you have 1 or more styles to change. It's more maintainable and readable.

If you really have the urge to do multiple CSS properties, then use the following:

.css({
   'font-size' : '10px',
   'width' : '30px',
   'height' : '10px'
});

NB!
Any CSS properties with a hyphen need to be quoted.
I've placed the quotes so no one will need to clarify that, and the code will be 100% functional.

Pass it as an Object:

$(....).css({
    'property': 'value', 
    'property': 'value'
});

http://docs.jquery.com/CSS/css#properties

$('#message').css({ width: 550, height: 300, 'font-size': '8pt' });