Hi,

If you go to Customize > Content, you can do something like this:

<p style="font-size: 30px;">Here goes your catchy header</p>

If you want to change the size of inline elements (without creating a separate paragraph), use <span> element, like so:

Tell the users that your website is not active yet. <span style="font-size: 30px;">Put the reason to subscribe</span> for the notification in this paragraph.

Let me know if this is what you’re looking for.