Fleet UI: Consistent on-hover effects

[RachelElysia]

Fleet version: (head to the "My account" page in the Fleet UI or run fleetctl --version)

Operating system: (e.g. macOS 11.2.3)

Web browser: (e.g. Chrome 88.0.4324)

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🧑‍💻  Expected behavior

Hovering over a "Cancel" button will have the same on-hover styling

💥  Actual behavior

Save query and save policy modal both have underline styling for on-hover of the cancel button. Elsewhere in the UI only darkens the word

TODO: Design clarify on-hover styling, Interface fix styling to be consistent across app

More info

[xpkoala]

@mike-j-thomas Do you have a preference on the cancel buttons having the underline when being hovered over?

[mike-j-thomas]

@xpkoala We don't need the underline, thanks.