Applying the Mushroom Shadow theme removes all theming

[cholywell]

When applying the Mushroom Shadow theme from https://github.com/piitaya/lovelace-mushroom-themes to the dashboard the timer-bar-card looses all theming.

type: custom:timer-bar-card
name: Alarm is arming. Exit the house!
entity: timer.alarm_arm_countdown
visibility:
  - condition: state
    entity: timer.alarm_arm_countdown
    state_not: idle
mushroom:
  color: red

The Mushroom Shadow theme adds a drop shadow effect to the cards. The only workaround is to remove mushroom: from the timer-bar-card yaml but then it looses it's mushroom theme and the drop shadow.