I mean this is a Plugin Named WoWpi.

Deactivate or edit this.

This issue coems from your theme CSS, it sets background color to all tables and this plugin tooltip table is also being affected. You can use this CSS code to overwrite theme affection. Put it in themes' style.css or in  Dashboard > Forums > Settings > Styles > Custom CSS Code textarea, then delete all caches and do Ctrl+F5 on front-end:

.wowhead-tooltip.wowhead-tooltip-width-restriction table{ 
     background-color:#111111!important;
}

Posted by: Robert

This issue coems from your theme CSS, it sets background color to all tables and this plugin tooltip table is also being affected. You can use this CSS code to overwrite theme affection. Put it in themes' style.css or in  Dashboard > Forums > Settings > Styles > Custom CSS Code textarea, then delete all caches and do Ctrl+F5 on front-end:

.wowhead-tooltip.wowhead-tooltip-width-restriction table{ 
     background-color:#111111!important;
}

This worked perfectly.

Thank you for taking the time to get back to me.