Color of "CANCEL" button in custom dialogs makes it appear to be disabled

[per1234]

Describe the bug

🐛 The background color of the CANCEL button on the File > Preferences and Select Other Board & Port dialogs makes it appear to be disabled.

🐛 The grayish color of the CANCEL button, as contrasted to the teal of the OK button next to it gives the visual impression that this button is not clickable.

To Reproduce

1. Select File > Preferences from the Arduino IDE menus.

🐛 CANCEL button appears to be disabled.

Expected behavior

Ideally, the style of the custom dialogs would be consistent with the IDE's other dialogs, which follow the OS conventions the user is already familiar with.

Screenshots

Desktop

• OS: Windows 10
• Version: 2.0.0-beta.1-snapshot.9e35571
  Date: 2021-02-12T08:28:48.914Z
  CLI Version: nightly-20210212 alpha [560025a6]

[per1234]

Closing as resolved by #991