Change the font size of post headings in side widget

Have put the 3 x home page widgets on to the side, with post links into one and now the headings are too big. The other 2 sidebar widgets are fine but the 3rd is where I have a linked posts list, so just want the text the same size as in the other 2 widgets. Could this be because I only have 3 posts? When inspected the elements from Chrome browser it said the H3 Font size was: 1.4rem; but when I checked on the CSS style sheet it said H3 should be 2em; is that right? sorry not keen on showing the link to website yet.
Anyhow, I am not developer so if you could guide me in the right direction that would be much appreciated.