Hi @devendra14321 ,
If you are looking to make text bold, I would use a label next to/above the control instead(https://help.nintex.com/en-US/nwc/Content/Designer/FormControls/Label.htm). There is current no way to use css in a NWC Form.
@devendra14321 There is a couple options but it may not be perfect, side by side looks a bit better.
The other option would be removing required and using a rule for validation instead.