The 'tab-strip-area top' part is not applied

[MonikaKirkova]

Description

The tab strip area top CSS part selector does not apply the styles. It is working in version 1.18.1

• version: 2.1.2
• browser: NA

Steps to reproduce

1. Create a Dock Manager layout with a pane that has a top tab strip area.
2. Add the following CSS:

igc-dockmanager::part(tab-strip-area top) {
  background: red;
}

3. Observe the top tab strip area.

Result

The background is not red.

Expected result

The background should be red.

[MonikaKirkova]

the 'pane-header-content', 'tab-header-more-options-button', 'tabs-more-menu-content', 'pane-header-close-button', 'tab-header-close-button' and 'tabs-more-menu-item' parts are not working as well