By default does the ui widget lightbox resize based on content?

By default does the ui widget lightbox resize based on content?

One of our vendors announced that they were going to increase the size of
our videos. Bigger height and width. They play the videos using jquery ui
widget. They said that we may need to look at the css (don't ask why they
are doing this) and make changes before the roll out. My impression was
that the ui widget lightbox resizes based on content but I wanted to make
sure.
If there is any changes that will be made we will have to add our own css
using !important tags to overwrite theirs.