Dark Theme Compatibility Updates

[DawoudSheraz]

This issue is part of the larger #116 work and focuses on the following two items:

• Adding dark theme support for Image Explorer problem type/xblock
• Add any remaining items to make ORA xblock completely compatible with dark mode

The image explorer was originally reported at openedx/wg-build-test-release#410. Due to limited time, it was not fixed and was mentioned to be catered to after sumac.1.

ORA xblock issues were reported in openedx/wg-build-test-release#402. While many of them were fixed in #111, some still remain (see the related issue for context). The above-mentioned issues should be fixed before sumac.2, which is planned for 9th Feb, 2025.