I found there is a very strange issue which there are two elements, input area and submit button in the subscription form adopted by fluent form, not to be aligned horizontally.
https://waamiya.com/wp-content/uploads/2022/10/subscription-form.png
Originally, I imported this section from Xstore demo data. Once I upgrade Xstore theme from version 8.3.4 to 8.3.5 then this stranged issue happened. Advise me how to revise it.