Background Image Not Applied To Div

Issue

I'm new to CSS and I wanted to add a background image to a div like this:

<div class="col-4 customBack">  
</div>

And here goes the background image:

.customBack{
    background-image: url("img/shadow3.png") !important;
}

But it didn't apply into the div and does not show the image as background!

So how can I show this background properly...

Solution

Is this what you want?

div {
  border: 2px solid black;
  height:300px;
  width:300px;
  background: url('https://picsum.photos/300/300');
}

<div></div>

Answered By - Deadpool