different font-weights for different h-tags ?

Hi,
via custom css I tried to have different font-weights for different h-tags. For example h2 = 800, h3-h6 =400.
In the customizer I set “font-weight=default” and added to custom css:
h3{font-weight:400 !important;}

But nothing happens, h3 stays also 800.

Can you please help?
Is there something going on in your original css or in the function.php that overwrites all my comands?