Description of problem:

In the RHDH, the EntityPeekAheadPopover component from @backstage/plugin-catalog-react renders with extra rounded corners on both the top-left and top-right edges.

This issue is not observed in the upstream Backstage implementation (v1.42.5). The popover styling in RHDH (v1.8.2) appears visually different, suggesting a possible theme override, global CSS override, or MUI styling conflict affecting the underlying Popover / Paper component.

Reference component:
https://github.com/backstage/backstage/blob/master/plugins/catalog-react/src/components/EntityPeekAheadPopover/EntityPeekAheadPopover.tsx#L78

NPM package:
https://www.npmjs.com/package/@backstage/plugin-catalog-react

Example Usage

The component can be rendered from any frontend plugin as shown below:

<EntityPeekAheadPopover entityRef={`user:${namespace}/${username}`}>
  <Chip
    variant="outlined"
    label={name}
    avatar={<Avatar alt={name} src="#" />}
  />
</EntityPeekAheadPopover> 

When hovering over the wrapped component (e.g., Chip) in RHDH, the popover shows additional rounded edges.

Prerequisites (if any, like setup, operators/versions):

• RHDH deployed or running locally

• Catalog plugin enabled

• @backstage/plugin-catalog-react installed

• Any frontend plugin rendering EntityPeekAheadPopover

Steps to Reproduce

1. Deploy RHDH 1.8.2 (or run RHDH locally).

1. Navigate to a page where EntityPeekAheadPopover is rendered withing any frontend plugin

1. Hover over the component (e.g., Chip).

1. Observe the popover UI styling.

1. Compare the same implementation in upstream Backstage 1.42.5.

Actual results:

• Extra rounded corners are visible on the top-left and top-right edges of the popover.

• Styling inconsistency

Expected results:

• No additional rounded edges.

Reproducibility:

Always

Build Details:

• Product: RHDH

• RHDH Version: 1.8.2

• Backstage Version: 1.42.5

• Component: EntityPeekAheadPopover

• Package: @backstage/plugin-catalog-react

Additional info (Such as Logs, Screenshots, etc):

Please attach comparison screenshots:

RHDH 1.8.2
– Shows extra rounded corners on top-left and top-right
 

vs

Backstage 1.42.5
– Expected corner styling (no extra rounding)

No console errors observed.
Likely related to MUI theme overrides or global CSS differences in RHDH affecting Popover → Paper styling.