[Bug Report][3.0.0] Expansion Panels have no rounded corners when having 1 single expansion panel component

[nerodark]

Environment

Vuetify Version: 3.0.0 Vue Version: 3.2.41 Browsers: Chrome 106.0.0.0 OS: Windows 10

Steps to reproduce

On load of reproduction link, the component has no rounded corners. When you expand, it does.

Expected Behavior

To have rounded corners when it's collapsed and contains 1 expansion panel component. Like it does when it's collapsed and contains multiple expansion panel components.

Actual Behavior

No rounded corners.

Reproduction Link

https://play.vuetifyjs.com/#...