I am having trouble applying a style that is !important. I’ve tried:
$(\"#elem\").css(\"width\", \"100px
I would assume you tried it without adding !important?
Inline CSS (which is how JavaScript adds styling) overrides the stylesheet CSS. I'm pretty sure that's the case even when the stylesheet CSS rule has !important.
Another question (maybe a stupid question but must be asked.): Is the element you are trying to work on display:block; or display:inline-block;?
Not knowing your expertise in CSS... inline elements don't always behave as you would expect.