width input fields on form in multisite

I use contactform7 on a multisite I’m building (offline for now). The width of the input fields is very small (just room for about 15 characters), and whatever I do, I cannot change it. Other changes (like font color of background color) will show, but not the width of the fields.
I tried
* css in customizer
* css in child theme
* adapting fields in contact form itself
* plugin cf7
* switching to hueman theme instead of the hueman child theme
* When I switch to another theme, the width of the fields is normal.
* I disabled every other plugin, but nothing will change the width.

On an offline single site I use for testing plugins, the setting for width works fine, so I suppose it has to with something in the Hueman theme when using it in multisite.

I hope someone can help me on this.