Fix frontend issues following CSS update

What does this MR do and why?

• Fixes frontend JS/CSS issues where "bottom half" would not show for a non-upload zip import following CSS changes

How to set up and validate locally

• Click "select root dir" after inputting a valid path to "import zip". The import button will never be enabled.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• Have you checked this doesn't interfere/conflict/duplicate someone elses work?
• Have you fully tested your changes?
• Have you resolved any lint issues?
• Have you assigned a reviewer?
• Have you applied correct labels?