0.116.4 - Failed to resolve module specifier "card-tools/src/lit-element".

My Home Assistant version: 0.116.4

My lovelace configuration method (GUI or yaml): GUI

What I am doing:

• I installed the Javascript Module card-mod.js according to the description Lovelace Plugins
• Then I changed the Entities Card Configuration in the Lovelace UI as follows:

type: entities
style: |
  .card-header .name { 
    color: red;
  }
entities:
  - entity: input_select.radio_station
  - entity: input_select.dlna_render
  - type: divider
  - entity: script.local_radio
title: Radio Stationen

What I expected to happen:

• The title “Radio Stationen” be in red

What happened instead:

• The title color remains black
• The log (log level info) shows the following entry:

2020-10-27 13:57:08 ERROR (MainThread) [frontend.js.latest.202010012] https://homeassistant.local:8123/lovelace-prod/default_view:0:0 Uncaught TypeError: Failed to resolve module specifier "card-tools/src/lit-element". Relative references must start with either "/", "./", or "../".

Minimal steps to reproduce:

• Update Home Assistant to version 0.116.4
• Install card-mod-js according to the description
• Create a new Entities Card in Lovelace with a title

# The least amount of code possible to reproduce my error
type: entities
style: |
  .card-header .name { 
    color: red;
  }
entities: []
title: Hallo World
# End of code

Error messages from the browser console: Uncaught TypeError: Failed to resolve module specifier "card-tools/src/lit-element". Relative references must start with either "/", "./", or "../". (default_view:1)

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[X] Have made sure I am using the latest version of the plugin.

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[hyperant]

Had the same issue, make sure you get the correct card-mod.js file. The file I got was from src/card-mod.js

I then noticed there is a card-mod.js file in the root of the project, looked at the source code for that and noticed it was different. Updated my card-mod.js file to that one instead and it all just started to work.

https://github.com/thomasloven/lovelace-card-mod/blob/master/card-mod.js

[buentead]

The solution of @hyperant fixes this issue.