See this screenshot:

The search box has zero distinguishing visual features to help people find it. It is so hard to notice this text that I almost concluded (with great irritation) that you simply could not search the npm docs. The problem is that I expected a normal search box control and so when I was visually skimming the header bar, I skipped over the "Search npm Docs" text completely. I'm not going to actually read all of the links in the header bar; I'm going to look specifically for the control that I expect to be there, that looks a particular way in every other website or app.

This problem is made worse by the fact that the links in the header bar don't look very distinctive to begin with: they're not blue, and they're not even underlined. They look like completely normal text and the only clue that they might be clickable is that they're in the header bar. This is not very good UX, and it further serves to make the search box indistinguishable.

Putting a box around the search bar would help. Putting a magnifying glass icon next to the text would also help.