Browsers don’t always display websites or fonts the same. With fonts, it is partly dependent on what fonts are installed on the local computer, unless the site is using web fonts. Do some background research on fonts for websites and you’ll learn more. You can change the fonts — usually in Theme Options or if not there, in the CSS code.
But for your particular theme, since it’s a commercial theme from Elegant Themes, you’ll need to contact them for help.