Hey I just customized this myself today so I may be able to help with the CSS. If you just want to increase the width to a set value it would look like:
:root {
--center_content_width: 1500px;
}
But if you wanted the width to be a percentage of the page width you can inverse the --app_content_width formula and calc your desired % minus the other stuff that will be added:
:root {
--center_content_width: calc(100% - calc(var(--center_content_padding) * 2 + var(--wiki_box_width) + var(--wiki_box_margin)));
}
In either case you may also want to set the widgets to a smaller static width or you can get some really large image/video result panels:
.widgetContent {
max-width: 1000px;
}
One can also combine these and say "a percentage of the page up to a certain limit":
:root {
--center_content_width: max(calc(100% - calc(var(--center_content_padding) * 2 + var(--wiki_box_width) + var(--wiki_box_margin))), 1500px);
}