How to properly customize the bootstrap grid for a responsive page?

Question

css

There is a ready-made layout of this type with the Bootstrap3 library connected via Webpack.
It is necessary to make a grid of the following width:
aside - 200px;
main content blocks of 250px each.
Distance between blocks -15px;
Max width -980px;
When reducing the width, the blocks should adapt to the screen size
How to layout correctly in this case so as not to break Bootstrap and set the required sizes

Answer 1

Aside should also decrease?
It's just that usually the menu columns are kept in the same width. And on small screens, they either disappear, or hide under the button, or move under the content.
I would make the aside constant, and inside the content area .col-md-4 for each block.