This commit improves the user interface in modal display.
- Prevent layout shifts caused by background scrollbars when modals are
active.
- Fix unintended overflow of modals on small screens, preventing parts
of the modal from being cut off on the right side.
- Refactor DOM manipulation, enhancing modularity, reusability,
extensibility, and separation of concerns.
- Centralize viewport test scenarios for different sizes in a single
definition for E2E tests.
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