Hello davout,
If you want to change the size of the font then you should use the approach below:

#password {
--smart-font-size: 20px;

More details you could find in the page below:
About the case with the password, I would like to suggest you use the Smart.PasswordTextBox.
Please, take a look at this demo:
Best Regards,
Hristo Hristov
jQWidgets team