Cart/Checkout: Apply btn on coupon component does not follow corner radius of other buttons

[garymurray]

Describe the bug
The Apply button on the coupon component does not follow the styling of the other buttons - it has a square radius, whereas the proceed to checkout and place order buttons are rounded.

[haszari]

Note also the cart Proceed button is also square on front end:

[Aljullu]

I'm seeing the same as @haszari. What theme were you using @garymurray?

Both of them inherit the border-radius from the theme (.button selector). The difference might come from the fact that Apply is a <button> but Proceed to Checkout is a <a>, so if a theme only styles <button> elements but not element with the class button, there might be some discrepancies in the style.

[garymurray]

I was using Storefront - note the rounded corners on the place order button vs the square one on the apply button in the checkout page:

[haszari]

In #2390 I've fixed this by removing our lone opinionated style for the place order button radius – the idea is that the theme is responsible for button roundedness, and we defer to theme.

Keen for feedback - cc @garymurray @Aljullu. Another alternative would be that we always round the cart/checkout buttons, essentially overriding the theme styles.