Environment
Provide version numbers for the following components (information can be retrieved by running tns info in your project folder or by inspecting the package.json of the project):

• CLI: 8.0.1
• Cross-platform modules:
• Android Runtime:
• iOS Runtime:
• XCode Version:
• Plugin(s):

Describe the bug
background attribute set in css on ActionBar is being applied normally on Android, but not on iOS.

ActionBar {
	background: linear-gradient(180deg, rgba(0, 115, 150, 0.85) 0%, rgba(25, 160, 172, 0.85) 100%);
	color: white;
	padding: 0;
}

Android screenshot:

iOS screenshot:

The ActionBar is still there on iOS and I am able to alter the background color with background-color: black;, but I need to set the background color with a gradient color value and only background attribute supports gradient color.