How do i assign a class to a html image with css?

This is the html part:

.bild{
  height:100px;
  width: 100px;
}

<div class = "wrapper">
    <img class = "bild" src="https://placeholder.com/wp-content/uploads/2018/10/placeholder.com-logo1.png" alt="the google logo" > 
</div>

They do not seem to "understand" each other, as the image does not change.