MediaWiki:Common.css

Note: After publishing, you may have to bypass your browser's cache to see the changes.

Firefox / Safari: Hold Shift while clicking Reload, or press either Ctrl-F5 or Ctrl-R (⌘-R on a Mac)
Google Chrome: Press Ctrl-Shift-R (⌘-Shift-R on a Mac)
Internet Explorer / Edge: Hold Ctrl while clicking Refresh, or press Ctrl-F5
Opera: Press Ctrl-F5.

/* CSS placed here will be applied to all skins */

body.page-Main_Page {
    background: url('https://predictive-pulse.com/path/to/your/image.jpg') no-repeat center center fixed;
    background-size: cover;
}