Appearance >> Customize >> Typography  Settings >> Font Sizes for Titles – Section

From this option, you can change the font size of titles. Please check the following instructions about titles font size.

• Heading h1 tag – please choose font size there for h1 tag on frontend.
• Heading h2 tag – please choose font size there for h2 tag on frontend.
• Heading h3 tag – please choose font size there for h3 tag on frontend.
• Heading h4 tag – please choose font size there for h4 tag on frontend.
• Heading h5 tag – please choose font size there for h5 tag on frontend.
• Heading h6 tag – please choose font size there for h6 tag on frontend.
• Post Title – Please choose font size there for post title on single post.
• Page Title – Please choose font size for page title on single page.
• Widget Title – This font size for widget title to the entire website.
• Comment Title – This font size for single post comments title.