[SOLVED] How to remove "Successfully logged back " messag

That message is being shown by the using the built in Joomla Notifcation/Error message system. If it's showing up badly, then other components will likely be showing up badly too. Here's my suggested fix:
In your template, there's the following line: <jdoc:include type="message" />. Whenever any component has a notification or message to display, this is where it will display in your template.

What you should do, is update your template file to include the system.css file which has default stylings for the error/notification messages. You can do this by adding the following line to your template file.
<link rel="stylesheet" href="/templates/system/css/system.css" type="text/css" />
Alternatively, you can copy most of the styles from that file into your template's css file and modify them to look good for your site.

Finally, if you really don't like it, you can remove that jdoc line, but we wouldn't recommend it as notifications are important for the end user from many components.

Hope this helps.