chrome is injecting some stylesheet in popup ui which reduces the font size to 75%

Question

I'm designing the popup UI of the extension, default font size of browser is 16px and when I view the design outside the extension environment the default font size is 16px, but when I open the UI, chrome injects some stylesheet which reduces the font size to 75% which is equal to 12px.

How can I prevent this behaviour?

check my screenshot below.

Ianteen

Solved the issue by setting font-size property's value to initial. But I still want to know why this happens with browser? – Ianteen

It's a bug. Chrome adds this style to reuse the system font since 2014, but it calculates the font size wrong. – Nunez