How to reset formatting to default font size (12)?

How to reset formatting to default font size (12)?

Hello,

I've set the default font size for my replies in Zoho Desk to 12, but if I click the "Clear formatting" button, it switches the font size to 10 (which is the default for Zoho). 

How to configure Zoho Desk to use my customized default font size (12) for the "Clear formatting" command?

Thank you!