Fix issues which Biome detected

[onnimonni]

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Context

I'm using Biome locally with my editor and it warned about couple of issues:

• useImportType
• useButtonType
  • This fixes accessibility issue too
• noUselessElse
• noArrayIndexKey

I hope these are useful for others as well 👍

Because the button element didn't have any styles yet I needed adjust css a bit too.

Screenshots