How to change the background colour of a Calc cell to a grandient.

[wynn.daybreak]

The options for background colour include Custom Colour but not Gradient.
Below, what I want:

[fpy]

same idea → 70384 – [FORMATTING] Patterns not available as cell background for tables
→ Arriere plan dans un tableau - #3 by fpy

→ create a gradient image and set it as cell background