When typing in the text boxes i cannot see the text as it is hidden behind the black sidebar.
This doesn't happen on a default install, so it's probably a styling issue caused by a plugin (or a site module in Craft 3) that injects CSS or JS into your site. Without context, it's impossible to tell which one. To debug this:
- If you don't already have a development environment, copy your site to a development environment so you can safely debug this issue.
- In your development environment, go through your active plugins and disable them one by one, checking if the control panel goes back to normal in between (make sure to do a full reload with CTRL + SHIFT + R / CMD + SHIFT + R). This will help you find out which plugin is injecting the broken styles.
Once you know where the broken styles are coming from, you can see what you can do to fix it from there. Maybe the plugin just needs an update. Maybe the plugin is outdated and doesn't work with your Craft version anymore, in this case you will need to remove it and/or find a replacement.