Igniteui-angular: [igx-grid] filter row menu transparency issue

[ig-robstoffers]

Description

When setting the $header-background theme to a color with some transparency opening the filter row menu results in being able to see through it.

• igniteui-angular version: 7.3.1
• browser: Chrome 75.0.3770.80

Steps to reproduce

1. Go to https://stackblitz.com/edit/angular-bpkxrh
2. Click on filter chip under first column header

Result

You can see through the filter row menu.

Expected result

The filter row menu should probably ignore transparency so you don't see what is behind it.

[mpavlinov]

@desig9stein The reported version is 7.3.x, but I don't see a PR for 7.3.x branch. Is that on purpose?

[desig9stein]

@mpavlinov no, I will create a PR for 7.3.x