W3 Schools HTML - Contains an excellent step-by-step tutorial, as well as a comprehensive tag reference.
W3 Schools CSS - Just like HTML, walks through a number of the common styling options and includes a comprehensive reference.
Bootstrap - CSS framework used in much of the TOM Toolkit via a specific PyPi package. The site contains a tutorial on the built-in CSS styles available for use.
django-bootstrap4 - Reference guide for the PyPi package that provides Bootstrap4 elements in Django.
Official Django Docs - The first-rate official documentation of Django. If you’re unfamiliar with Django, start with the step-by-step tutorial. If you’re looking for a reference, the docs contain topic-specific guides, “recipes”, and API documentation.
Django Girls Tutorial - If the official Django tutorial is more technical than you prefer, check out Django Girls. If you know Python and are just looking to familiarize yourself with Django, start with the “What is Django? chapter.
Classy Class-Based Views - Inheritance can be confusing. The CCBV reference page shows the class hierarchy of Django’s built-in class-based views, along with the available attributes and methods, and the class they each come from.
Databases - Information on setting up different database backends in Django.
Security in Django - Make sure your Django application is secure.
Dive Into Python - For anyone looking for a Python refresher.
Official Python Reference - Naturally.