Hi Ernst,

If you don't know previus URL - by default is not possible, becuase you have to put URL.

But you can always use HTML code inside Raw HTML addon, here is example code:

<button onclick="history.back()">Go Back</button>

Yes, supported by all popular browsers.

Preceding your 2nd question about whether the bg color of the button can be different, of course, you can specify it using button class names, for example, Bootstrap 5.x custom button styles:

<button class="btn btn-primary" onclick="history.back()">Go Back</button>

<button class="btn btn-secondary" onclick="history.back()">Go Back</button>

<button class="btn btn-info" onclick="history.back()">Go Back</button>