I love the dynamic stuff (but could be better signposted)

[jackbridger]

To reiterate it is so cool how you pull all of the line names dynamically and add the shadow class dynamically.

Some key lines:

const shadowedNames = [
  "hammersmith-city",
  "circle",
  "victoria",
  "waterloo-city"
];

function requiresShadow(lineID){
  return shadowedNames.includes(lineID);
}

let shadow = requiresShadow(line.id) ? "tube-line-shadow" : "";
li.classList.add("tube-line-li");

 li.innerHTML = `
    <span class="tube-line-name line-${line.id} ${shadow}">${line.name}</span>

I took a lot of inspiration from this thank you. It took me a while to understand though so maybe it could be a little clearer signposted? E.g. clearer name of 'shadow' or comments above the helper functions or some comments in the feature-tube request call as quite a lot going on. Or maybe more helper functions in there to shorten that call.