You should give .bb3 a background using repeating-linear-gradient. I don’t what i am doing wrong, it is showing the same error.
.bb3 {
width: 10%;
height: 55%;
background-color: var(--building-color3);
background: repeating-linear-gradient(90deg,
var(building-color3),
var(building-color3),
var(window-color3) 15%);
}