Insufficient text contrast in header element

[radkostanev]

Describe the bug
When a theme color/variant setting has been set to the card which is different than the default one in conjunction with a dark theme, the text within the header element does not have enough contrast and is thus hardly readable.

Note we have tests for the variants, but these do not include the header element: https://github.com/telerik/kendo-themes/blob/develop/tests/_output/default/card/card-variants.png

To reproduce
Steps to reproduce the behavior:

1. Go to https://dojo.telerik.com/ezOpOfez/4
2. Observe the color of the text within the header

Alternatively,

1. Go to https://demos.telerik.com/blazor-ui-dev/card/appearance
2. Switch to the default dark theme
3. Start changing the ThemeColor value through the drop-down in the configurator. Notice that the card is practically the same(arguably a different issue, as the theme color does not apply at all in the dark theme)

Expected behavior
Text should have enough contrast despite the settings of the component and the theme.

Screenshots

Affected package (please remove the unneeded items)

• theme-default

Affected suites (please remove the unneeded items)

• Kendo UI for jQuery
• Kendo UI for Angular
• Kendo UI for React
• Kendo UI for Vue
• Telerik UI for Blazor

Affected browsers (please remove the unneeded items)

• All

Build system information (please remove the unneeded items)

• Not Applicable