[css] How to rotate the background image in the container?

Update 2020, May:

Setting position: absolute and then transform: rotate(45deg) will provide a background:

_x000D_
_x000D_
div {_x000D_
  height: 200px;_x000D_
  width: 200px;_x000D_
  outline: 2px dashed slateBlue;_x000D_
  overflow: hidden;_x000D_
}_x000D_
div img {_x000D_
  position: absolute;_x000D_
  transform: rotate(45deg);_x000D_
  z-index: -1;_x000D_
  top: 40px;_x000D_
  left: 40px;_x000D_
}
_x000D_
<div>_x000D_
  <img src="https://placekitten.com/120/120" />_x000D_
  <h1>Hello World!</h1>_x000D_
</div>
_x000D_
_x000D_
_x000D_

Original Answer:

In my case, the image size is not so large that I cannot have a rotated copy of it. So, the image has been rotated with photoshop. An alternative to photoshop for rotating images is online tool too for rotating images. Once rotated, I'm working with the rotated-image in the background property.

div.with-background {
    background-image: url(/img/rotated-image.png);
    background-size:     contain;
    background-repeat:   no-repeat;
    background-position: top center;
}

Good Luck...