Paralax section size

Hi there !
(Please excuse my english, as it is not my main language)

I’m using Shapely in local with a child theme. As I won’t be the final user of the website, I’m trying to make it as “friendly” as possible to someone completely neophyte to administrate it.
Thus, I’m considering using a plugin allowing me to use parallax sections widgets in one page. The idea is to use the bootstrap grid to get an image on one side and text on the other side. But I’d like to change the grid size.

For now, if I chose let’s say to but my image on the left, the grid will have a col-md-8 class and the text a col-md-4. What can I do to make it md-6/md-6 ?

Thanks in advance !

Hey there

Sorry, this is not possible to add any new class to exiting elements of the theme without customization, however I can help you with some custom CSS, so, if CSS is enought then please provide a link to the page and just show me what exactly you want to achieve