Hello There,
The v2 headline element has its own default settings. When using the builder, you can change the font size of the v2 headline in the headline element settings. The v2 element is independent from the default theme styles unlike the classic headline which depend only to the global settings. If you use h2 and h3 tags, this will also use the default theme styling. You can only override it by using a custom css. You may add the following CSS code in the X > Theme Options > Global CSS (http://prntscr.com/evui3r)
h2, .h2 {
font-size: 30px;
}
h3, .h3 {
font-size: 24px;
}
This code will specifically style heading tag elements when you insert some thing like this in the editor:
<h2> The sample title</h2>
<p>Quisque vel lectus efficitur, dictum libero malesuada, eleifend justo. Phasellus efficitur eros metus, nec convallis ipsum bibendum vitae. Nulla non mollis ante. </p>
<h3>In vel massa porta, euismod orci in, venenatis nisl.</h3>
<p>Mauris congue nec tellus eget tristique. Fusce scelerisque aliquam tincidunt. Quisque et ex quis lectus ullamcorper congue. Aliquam non metus purus. Mauris ut ligula metus. Vestibulum nec ullamcorper ex. Nulla tincidunt consequat feugiat. Nulla laoreet porttitor sapien, vel venenatis mi mattis in. Integer dapibus ut neque a dapibus.</p>
Hope this helps.