formBackground colour token applies to entire component container, not individual input fields

[quinnmidnite]

Summary

When setting formBackground via CheckoutComponents.ColorTokens, the colour is applied
to the entire component container rather than just the individual input fields. Additionally,
background appears to have no visible effect at all.

This contradicts the published documentation, which shows:

• colorBackground → the outer component container/surface (see annotated diagram)
• colorFormBackground → individual input field backgrounds only

In practice, formBackground is doing the job of background (colouring the entire
container), and background has no visible effect.

Reproduction

let colors = CheckoutComponents.ColorTokens(
    background: .red,          // Expected per docs: outer container. Actual: no effect
    formBackground: .lightBlue // Expected per docs: input fields only. Actual: entire container
)
let designTokens = CheckoutComponents.DesignTokens(colorTokensMain: colors)

Documentaion snapshots