The reason you are having the problem is because you have your website on localhost/folders. And you Drupal installation expects your website to be in locahost. So there is to easy ways to solve this problem. Either you move everything up directory and all your files are in the localhost.
cd /Applications/MAMP/htdocs/testwebsite # Move to the website folder directory. sudo mv * .[^.]* .. # Move everything up one directory. cd .. # Move to localhost directory. sudo rm -rf testwebsite # Remove testwebsite directory.
Or you can created a temporary soft link on your localhost so your Drupal installation can find the sites folder on the localhost.
cd /Applications/MAMP/htdocs/ # Move to the webserver directory. sudo ln -s testwebsite/sites sites/ # This is going to created the soft link .