How can I put all style in p tag

I can't use span or div tag in our system. only p tag is allowd.

so I put this code at config.js

config.font_style =
   {
   element: 'p',
   styles: { 'font-family': '#(family)', 'margin-top': '2px', 'margin-bottom': '2px' },
   overrides: [{ element: 'font', attributes: { 'face': null}}]
   };

   config.fontSize_style =
   {
   element: 'p',
   styles: { 'font-size': '#(size)', 'margin-top': '2px', 'margin-bottom': '2px' },
   overrides: [{ element: 'font', attributes: { 'size': null}}]
   };

If I set just one style (font or size). It works well. but If I can't change both one It remove pre-style.

For exemple,

TEXT : abc

When I change font to 12

abc

And then I chang font to Arial

abc

font-size: 12px is disappeard.

I want set source like this

abc

Is there any idea?