Monica is way beyond me in her depth of knowledge regarding how we're now able to define custom HTML tags, meaning components, with their own encapsulated behaviors, state and styling.
In the new HTML, which structures the document per the Document Object Model (DOM), we have what's called a "Shadow-DOM" tightly coupled to specific HTML tags. Defining web components involves stuffing little shadow DOM pockets with hidden functionality, though with the right developer tools you're free to crack in and read it.
If a website comes from a server it more than likely is talking to a server, that goes for phone apps as well. There's nothing open source about most websites other than the fact the tools to build them are open. Developers have made it easy to develop black boxes. That was never going to go away.
However by training on a lot of the same tools, we learn to hop around among the boxes, contributing within each, bringing the lessons from one to another.
Monica is a fantastic teacher and speaker.