Description

This PR reverts the rounded corners introduced temporarily before the latest releases.

At first, it was important to make people feel that there was a connection between something they already knew previously and the styles of the design system being implemented in the platform about a year ago.

This move was like a bridge to move people from point A to point B. Now that this is done, I'm mainly restoring the original proposal to ensure we can keep improving Mautic.

Why?:

• The redesign can now be moved forward faster;
• Carbon has playground to interact with elements, documentation, backed by UX research, components we could inspect to retrieve CSS code;
• It looks professional and serious, visually;
• We'll work on the textual side to make it playful;
• The final result will be more reliable, given the resources Carbon provides to replicate components (it's open source)
• Human resources are limited for planning, wireframing and coding to implement, so following something that already exists allows us to deliver a better result, quicker

These changes also have impact on accessibility; along the way, I've been implementing several enhancements that rely on how elements behave in this design system (giving fields enough contrast by adding a border at the bottom, for example), they're restored in this PR.

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📋 Steps to test this PR:

1. Open this PR on Gitpod or pull down for testing locally (see docs on testing PRs here)
2. Open several pages and check the squared look