I am making a website in wordpress and I'm using a paid template. The template comes with a bootstrap grid. The issue I have is editing some css code, because I can't find the source of the css codes. 
As you can see on the screenshot, the media queries are located at grid-responsive.css. The code I want to edit is the css above it. I want to remove the padding-right: 30px !important; from .mpce-prvt-4661-5a018ae17a157:not(.mpce-dsbl-padding-right) and same for the left side.
But I can't find the css file and on the right side it doesn't tell me which file the source is. I searched in all the css files I have and couldn't find it. Someone having an idea how to locate it?
grid-responsive.cssis, it's about the css above it<style></style>(generated by JS or included by any plugin?). Try to find string 30px !important in whole directory, you'll find where it's generated..mpce-prvt-4661-5a018ae17a157it'll be an inline style<style>with id='template-name'-private-styles. So what @sébastien-gicquel is saying is the answer