Focused toggle button shows inner white border

[GCHQ-Developer-847]

Summary of the bug

When you focus on a toggle button when it is selected, it shows a white inner border which doesn't match the designs.

🪜 How to reproduce

1. Click on a toggle button in dark mode - so it becomes focused and selected.
2. See that it displays a white inner border

📸 Screenshots or code

🧐 Expected behaviour

The white border should be black to match when it is not focused.