This is because the viewport width is in pixels and does not change with the font size.
Bootstrap gutter width.
Variables and maps determine the number of columns the gutter width and the media query point at which to begin floating columns.
In the case of the sm grid your container class will 970px 940px grid gutter width.
Bootstrap grid is a system of columns and rows which is used for creating a page layout.
While bootstrap uses ems or rems for defining most sizes pxs are used for grid breakpoints and container widths.
See how aspects of the bootstrap grid system work across multiple devices with a handy table.
Every column have a padding of 15 px on both sides.
The biggest difference between bootstrap 3 and bootstrap 4 is that bootstrap 4 now uses flexbox instead of floats.
In bootstrap 3 the gutter is defined as 30px 15px on each side of a column.
Thanks for the response.
Every column get a width of 940 12.
The resulting grid gutter width 2 on both sides of the grid will be hide with a negative margin of 15px.
One big advantage with flexbox is that grid columns without a specified width will automatically layout as equal width columns.
Which makes a gutter between of 30 px.
Mobile friendly responsive and can be rearranged depends on screen.
30px 15px on each side of a column 30px 15px on each side of a column.