Either way, if you don't put text within the <div class="bg"></div> then the background image will not show (I checked this in version 4.5).

You will then need to put a fixed height (commented as full height) on the image such as:

height: 50vh;

I also think you have a syntax issue in your css... should it not be

background: url("/PWDMDB/img/poweronbg.jpg")no-repeat center center fixed;

Try the code from out documentation - https://mdbootstrap.com/css/bootstrap-background-image/.

CSS:

body, html {
height: 100%;
}

.bg {
/* The image used */
background-image: url("https://mdbootstrap.com/img/Photos/Horizontal/Nature/full page/img(20).jpg");

/* Full height */
height: 100%;

/* Center and scale the image nicely */
background-position: center;
background-repeat: no-repeat;
background-size: cover;
}

HTML:

<div class="bg"></div>