Getting started with custom cards: and failing

Configuration Frontend
1

Hello,

My level: complete HA newbie, trying to add a custom card.

I want to add the slider-button to my installation.
(GitHub - mattieha/slider-button-card: A button card with integrated slider)

So, running HA in a docker container,
I copied the slider-button-card.js to /config/www/slider-button-card.js

I restarted HA

Added a resource:

image
image2154×574 11.9 KB

When I try to add :

image
image2154×574 47.3 KB

Any ideas what I overlooked ?

THanks!