enhancement: custom background

[Jay-Karia]

Is your feature request related to a problem? Please describe.

Adding a custom background to the card.

Describe the solution you'd like

We can add a new feature to add a custom pre built background to the card, with the user having options to choose from.
There could be different types of background such as textures, gradients, and so on...

Additional context

We can add a new API parameter: &custom_bg= to add the background.