librandi Yes, You can copy the CSS in \templates\ja_space\css\custom.css
file however, it might be required to add !important directive which will ensure that the specific CSS rule-set will apply.
The CSS which can be added is :
@media (min-width: 992px) {
.col-md-3 {
width: 20% !important;
}
}
@media (min-width: 992px) {
.col-md-9 {
width: 80% !important;
}
}
although, if you are looking forward to have sidebar-2 width changed for certain menu items, You may let us know enabling us to suggest more convenient and precise method which wont affect other pages or bootstrap grid system globally and yet, derive the results as envisaged