How can we overlap two images using css style?

.under {
  position: absolute;
  left: 0px;
  top: 0px;
  z-index: -1;
}

.over {
  position: absolute;
  left: 40px;
  top: 10px;
  z-index: -1;
}

<img src="https://tafttest.com/184x46.png" width="184" height="46" class="under" />
<img src="https://tafttest.com/100x84.png" width="100" height="84" class="over" />

You could use position:relative and set right:30px, bottom:30px, that would shift it up and left by 30 pixels.

CSS:

.icon{
position:relative;
right:30px;
bottom:30px;
}

The element you want to be on top needs to have a higher z-index

So the small icon would have a z-index of 2 and the images would have a z-index of 1

Example:

.icon {
  z-index: 2;
  position: relative;
  left: 30px;
  top: 30px;
}

.images {
  z-index: 1;
}