Bugfix: DCC redesign feedback from rc4

[KoolADE85]

This PR addresses the feedback collected from rc4:

General:

• Bolder (thicker) outline when components are focused
• Small adjustments to default colours so that WCAG colour contrast requirements are met
• Font family & font size consistently inherit from overall page font/size

Dropdowns:

• Hide radio buttons in single-select dropdowns
• Allow Backspace and Delete keys to clear selection

Input:

• Fix type=number increment/decrement buttons could appear disabled even though they are not

[github-actions]

Thank you for your contribution to Dash! 🎉

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[T4rk1n]

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