Shadow Background picker shows black background preview palette in Customizer

[aryanrajseo]

Base Styles > Global. Drop Shadow preview background became black while selecting some background color from color palette.

Found same shadow issue on

• Base styles > Buttons.
• Header > Primary Header shadow.
• Sidebars > Primary sidebars
• Sidebars > Secondary Sidebars

[seothemes]

Fixed with hardcoded CSS to force the background color.