Need a Watermark on a page

I have a dialog that has a Field Set. I want to place a watermark on that page or within the Field Set. I have tried with CSS and it didn't seem to work. I have also tried to add a background image in the images folder and for the Fieldset add the Style="background-image: watermark.png" using an image and that didn't work. Any suggestions???

DIV info on page

My Text Here
CSS Info .watermark { position: absolute; bottom: 0; left: 0; transform: rotate(45deg) translate(0, -80vh); font-size: 48px; color: #ccc; z-index: -1; }

This isn't the valid CSS syntax to specify a background image. You should use something like this if the image is in the wwwroot/images directory of your app:

Style="background-image: url(/images/watermark.png)"

That worked but not exactly what I wanted. It put the image more than once.

You also need to set background-repeat to none if you don't want it to repeat.