i want for odoo 10

There is no much difference between v10 and v11, so you can refer the above code

that module is for theme niyas but ii want to change font size this is the client requirement

yes that module is a theme and it have a feature to change the font from the front end, dont take the module as such, go through the code and see how the font is changed and do the same in your case

when i am installing this module it shows this error

field = target._fields[name]

KeyError: 'website_id'

if you are installing the v11 module in v10, you might get some error, make sure that you are installing in the same version

currently i am using v10 but that application doesnot available there in v10

If you have odoo11 install it in it and see, else check the code of the module and see