Some help wit custom CSS please

Hello,
I would like some help with the custom css in the form.
Page: https://www.domeintest.eu/speeltuin/index.php/contact
Please see the attachment for the font-weight. In the backend it is okay, but the frontend is too thick.
I used this code:
.ba-input-label-wrapper { font-weight: normal!important;}

Could you help me please?
Regards, Peter

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