What you should be able to do now

Go through this list honestly. For each one, decide: could you do this right now, in front of someone, without looking it up?

The browser: trace a request from DNS to first paint and say which parts your code owns. Read a Network waterfall and say what is blocking what. Name what a given CSS property costs in pipeline stages. Move first paint earlier by rearranging tags.

HTML: produce a correct semantic document with a valid outline from scratch. Predict what a browser builds from malformed markup. Choose the element that already does the job. Say what a screen reader will announce for a snippet, and check it. Build a form that validates with no JavaScript.

CSS: state the cascade steps in order and diagnose an unapplied rule without guessing. Calculate specificity by hand including :is and :where. Say whether a property inherits. Use the four cascade keywords correctly. Choose between flex and grid on the basis of the problem. Build a responsive layout with fewer than three media queries.

Mobile and the DOM: explain why 100vh overflows and fix it. Write srcset and sizes and predict which file gets picked. Prevent layout shift from images. Describe event flow and use delegation. Explain forced synchronous layout and restructure a loop to avoid it.

And the one that is really the point: look at a piece of generated markup and CSS and say specifically what is wrong with it, with reasons, not vibes, and then fix it.

If you can do most of these, submit. If there are three or four you cannot, go back and do those chapters properly rather than rereading them; the instruments are where the gaps close. And if there is one you cannot do, submit anyway and say so in the write-up. An honest gap is a much better signal to a reviewer than a confident bluff, and they will tell you where to look.