Invisible Continue Setup button on "Set up application page"

Shopify Partner
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I am having an issue on "Set up application page" if you check my screenshot, I have highlighted an area where hyperlink button exists but due to some CSS issue its font color and background is not set

I am unable to find the following file anywhere for editing " 

FYI: this page can be accessed by "{{ shopify domain }}/admin/api/auth?api_key={{api_key}}"

does anyone know how could I fix this issue?