Oh-list-card background-color - header

@JustinG you are my hero. Thank you very much. You showed me the right direction in similar problem here.

Do you have a hint for me, where I can read about such features/syntax an to use it in correct manner, like

  stylesheet: >
    .card-header {
      background: green
    }  

as I didn’t found any sources here.

BTW: I just used it in an oh-label-card too

component: oh-label-card
config:
  stylesheet: |
    .card-header {
      background: linear-gradient(to bottom, #6fa8dc 0%, #ffe74c 100%)
    }
     .card-footer {
      background: linear-gradient(to bottom, #6fa8dc 0%, #ffe74c 100%)
    }
  background: "linear-gradient(to bottom, #6fa8dc 0%, #ffe74c 100%)"
  fontSize: 28px
  footer: ="momentane Distanz ist. " + items.esp_amica_01_dist.displayState
  icon: '=(items.esp_amica_01_dist.state > 230) ? "oh:cistern-0"
    :     (items.esp_amica_01_dist.state > 50) ? "oh:cistern-60"
    :     (items.esp_amica_01_dist.state > 21) ? "oh:cistern-100" : ""'
  item: esp_amica_01_dist
  label: =Number(6000 - ( 6000/230) *
    (items.esp_amica_01_dist.state-20)).toFixed(0) + " Liter"
  title: Zisterneninhalt
slots: null

Cheers,
Peter