Hi Peeyush,
I have checked font is getting changed in IF_BSP_ELEMENT~DO_AT_BEGINNING of CL_HTMLB_INPUTFIELD class
ex.
CONCATENATE html
` style="font-size:1.0em"`
Can you please use this class CL_THTMLB_INPUTFIELD instead of CL_HTMLB_INPUTFIELD and try if this works in your case.
Regards
Sumeet