Custom Theme: How to change drop-down menu background color?

Configuration Frontend
1

How do I change ONLY the background color for all drop-down menus?

The closest thing I could find to it is card-background-color which is supposed to change the card background color; however, for some reason, it also changes the drop-down menu background color… making text unreadable:

image
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I believe that the popular ios-themes theme variety pack also has this issue since they have transparent card backgrounds.

I tried to figure this out using developer tools in my web browser, however, every time I click on the element selector, the drop-down menu loses focus.

2 
  input-fill-color:

The others:

### Inputs ###
  input-ink-color: 'var(--primary-text-color)'
  input-label-ink-color: 'var(--secondary-text-color)'
  input-disabled-ink-color: 'var(--secondary-text-color)'
  input-fill-color: 'rgba(0, 0, 0, 0)' # transparent
  input-dropdown-icon-color: 'var(--primary-text-color)'
  input-idle-line-color: 'var(--secondary-text-color)'
  input-hover-line-color: 'var(--primary-text-color)'
  input-disabled-line-color: 'var(--disabled-text-color)'
  input-outlined-idle-border-color: 'var(--disabled-text-color)'
  input-outlined-hover-border-color: 'var(--disabled-text-color)'
  input-outlined-disabled-border-color: 'var(--disabled-text-color)'
  input-disabled-fill-color: 'rgba(0, 0, 0, 0)' # transparent
3

Thanks @tom_l However, the real problem is that card-background-color is interfering with the color and transparency for drop-down menu background, I just want card-background-color to change card background color, nothing else that is unrelated.

Is it possible to use card-mod to prevent card-background-color from affecting drop-down menu background?