Zakra provides you various filter hooks to modify the typography option of Customizer. They are listed as below:

zakra_base_typography_heading_filter : Add your code to Base Typography.

zakra_typography_page_title_filter: Add your code to Page/Post title typography.

zakra_typography_h1_filter: Add your code to Heading 1 typography.

zakra_typography_h2_filter: Add your code to Heading 2 typography.

zakra_typography_h3_filter: Add your code to Heading 3 typography.

zakra_typography_h4_filter: Add your code to Heading 4 typography.

zakra_typography_h5_filter: Add your code to Heading 5 typography.

zakra_typography_widget_heading_filter:Add your code to Widget heading typography.

zakra_typography_widget_content_filter: Add your code to Widget content typography.

To know how to use a hook, refer to this: How to use Hooks in Zakra Theme?
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