javascript - Why does the whole page refresh when I use jQuery to increase or decrease the font size? -

I have an HTML page, where clicking on the font size to reduce the font size and the same button amplify me Button is needed.

I am using jQuery like this:

  $ ("p"). CSS ("font-size", "20")  

However, when I do this, the size of the font probably increases for 2 seconds and then appears back to normal. The page is fresh after clicking on that button ... why is it?