Why can't I use background image and color together?

Question

What I am trying to do is to show both background-color and background-image, so that half of my div will cover the right shadow backg

Answer 1

Here's an example of using background-image and background-color together:

.box {
  background-image: repeating-linear-gradient( -45deg, rgba(255, 255, 255, .2), rgba(255, 255, 255, .2) 15px, transparent 15px, transparent 30px);
  width: 100px;
  height: 100px;
  margin: 10px 0 0 10px;
  display: inline-block;
}