Charge image displayed with strange white edges with other background colour

[maisun]

This is not a bug/feature request, but seriously need some help with the image.
I use card-mod to change the default background colour with the following css variables:

card_mod:
  style: |
    ha-card {
      ......
      --custom-card-background-color: var(--charger-card-bg-color);
      --custom-primary-color: var(--charger-card-bg-color);
      --custom-text-color: var(--charger-card-font-color);
      --custom-icon-color: var(--charger-card-font-color);
    }

It works almost perfectly except that I notice some strange white edges around the image (screenshot below).
Switch back to default background the edge are not there. So I don't if there is any trick to hide it and appreciate anybody who knows how to do that share the code. It's certainly possible as with original background colour the edges are not visible. Many thanks in advance!

[maisun]

Anybody else notice this? The default background colour works fine though