Twenty Twenty-One: missing styles for button[type=submit]

[slaFFik]

2021 theme has default styles for input[type=submit] but it does not have those same styles for button[type=submit].

So some plugins, that use button to submit the form on the front-end, are having CSS issues with 2021.

[slaFFik]

It looks like ​https://github.com/WordPress/wordpress-develop/blob/master/src/wp-content/themes/twentytwentyone/assets/sass/04-elements/forms.scss should be modified to include additional styles for button[type=submit] same as input[type=submit].
Not sure what to do with:

1. button[type=clear]
2. generic button without defined type - most likely apply the same as button[type=button] and button[type=submit].

[poena]

The button styles are found here:
​https://github.com/WordPress/wordpress-develop/blob/master/src/wp-content/themes/twentytwentyone/assets/sass/05-blocks/button/_style.scss

and

​https://github.com/WordPress/wordpress-develop/blob/master/src/wp-content/themes/twentytwentyone/assets/sass/02-tools/mixins.scss

I recommend changing this only after https://core.trac.wordpress.org/ticket/51927 which updates the buttons.

-There will always be themes that are unstyled, so it is safest for plugins to style their own elements.

[poena]

This image shows the missing styles for different types of buttons (on the front).

[poena]

style the <button> element

[poena]

With patch 52029 applied. (chrome, windows, front view)

[SergeyBiryukov]

In 49988:

Twenty Twenty-One: Add missing styles for <button> element.

Props poena, slaFFik.
Fixes #52029.