This is an extension that I would to have the basic needs in an extension. Hopefully the extension will be able to change the background of your chrome browser periodically, be able to have a timer, and a to do list.
To make an extension make a folder and name a file in it called manifest.json. Once you made that file put this code in the file:
'{ "manifest_version": 2, "name": "My Cool Extension", "version": "0.1", "content_scripts": [{ "matches": [ "<all_urls>" ], "js": ["jquery-3.3.1.js", "content.js"] }] } '