Custom Theme - Override Max-Content-Width (1100px) via PHP / WordPress Filter

Hi Jelmer,
thanks for your reply. I know that I can override / manipulate the DOM, but this should be only the last (dirty) option. If I add a new row it looks like this …

The default setting for “with” is fixed and “Fixed Width” is 1100. Where is this number stored and how could I change it?

I use a custom theme, so there are no options via Customizer available. I thought this value was stored as theme mod > ‘fl-content-width’ …

set_theme_mod('fl-content-width','1400');
echo get_theme_mod('fl-content-width',''); // 1400

but even if I change this value, nothing changes and BB stills uses 1100 as default.

Best Daniel