fix: hr and img tags shouldn't break with global css overrides

[Benehiko]

Fixes the <hr> and <img> tags when using a global css override to reset browser styling.

The <hr> tag will now have margin: auto on all sides, pushing it to be centered in the element and removing excess space top and bottom. This will cause a change in the Ory components which will reduce their overall height. It is a small change and shouldn't have much impact on the overall look.

Related Issue or Design Document

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• [ ] I have read the contributing guidelines and signed the CLA.
• [ ] I have referenced an issue containing the design document if my change introduces a new feature.
• [ ] I have read the security policy.
• [ ] I confirm that this pull request does not address a security vulnerability. If this pull request addresses a security vulnerability, I confirm that I got green light (please contact security@ory.sh) from the maintainers to push the changes.
• [ ] I have added tests that prove my fix is effective or that my feature works.
• [ ] I have added necessary documentation within the code base (if appropriate).

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