Filter field width not adapting to width

-- HikaShop version -- : 2.6.0

-- not sure if this should go in filters, or display category --
I created some filters on custom fields, and all looked just fine.
Now decided to add another filter on 'brand' field and the filter shows. However it is not adapting its size to the widest option in the filter option list, like the other thee filters..
Where did I go wrong ?
I can't recall setting width anywhere (and can't see where I could). It looks kinda anoying like this.
Placing the filters in 1 or 4 columns does not change the behaviour. The filter for 'brand' is not wide enough....
(Attached image has both views, 1 column and 4 columns)

I can't recall having done anything special to CSS, so don't understand the answer at this point.
In the HikaShop configuration the CSS is set to default.

So I don't see why filtering field of custom objects adapts it's width to the widest element in the list to choose from, and the filtereing field of standard product field 'brands' does not.

I don't understand that message then..... (probably my bad)
"you can see to deactivate the "chosen" setting in the HikaShop configuration"
Where can I do that ?
The link points to the image settings, but I don't have issues with an image, but with the field width of the filter itself.
It does not adapt (correctly) to the width of the fields that it shows causing a slider bar to appear inside the options listed in the filter....

Thanks very much, I understand it now.