Absolutely…. the sizing of headings are in the theme’s style.css file, but for the one you are asking about is located around line 233 and looks like this:
[code type=css]
h1.intro-title {
font-size:20px;
font-size:1.250rem;
line-height:22px;
line-height:1.375rem;
}
There’s two font sizes showing, one using the px size and the other using rem which is a relative sizing. The rem one will be the one that overrides the px because it follows right after the px. I use this tool to convert px to rem (also em) http://www.pxtoem.com but if you prefer px only, simply remove it and change the font-size for the px one.
Reminder: Whenever making modifications to core theme files, it’s recommended you use a child theme or for css only, if you have jetpack installed, it has a nice css editor that can be used so you don’t need a child theme for. But basically a child theme helps maintain any modifications a person does whenever there is an update to the main theme (parent theme) and won’t be lost on updates.
edit
h1.intro-title {
font-size:18px;
font-size:1.1250rem;
line-height:20px;
line-height:1.25rem;
}
but not effect
