Simple Welcome Bar is a dropdown bar at the top of your site to draw attention to a link or message.
Some themes use the CSS 'Z-Index' property to adjust placement of certain elements. To adjust the z-index override of Welcome Bar, open the settings page and change the 'Z-Index fix' value up until your problem is resolved. ex. change the default to 999999, 100000 or higher. This should fix this for most themes.