Adjusting the width of gallery captions

Site URL: https://dog-bassoon-3aty.squarespace.com/work/journalisme

Password : Audiosensible

Hi! 

I have just figured out how to custom a slideshow so it shows the image on the left and the caption on the right (it's at the bottom of the page).

I am now a little bit stuck as I am trying to add custom css in order to change the caption width. I ideally would like to expand it on the right so that it has the same padding as the other text blocks on the page. I've tried to work on the caption wrapper but no luck so far.

Does anyone have an input that could help?

Thanks a lot!

Thank you very much @tuanphan, this has been really helpful!