#1. First, you click on the Site Styles icon
#2. Next, you choose Fonts
#3. Scroll down to the bottom and choose Assign Styles
#4. Scroll down to BLOG POST – Pagination and Click on Heading
#5. Next, click Heading 3 in the Size option
#6. Next, choose Custom
#7. You can enter the custom size and click Save on the left of the Header
