Increase contrast of search input text in docs.

[bdice]

This PR increases the contrast of the documentation's search bar text so that the input text is legible.

If this PR is approved/merged, I will make a similar PR to improve Thrust's documentation. If anyone is aware of other instances of this issue, let me know and I can make corresponding updates to other repositories.

Before:

After:

[wmaxey]

I'll take a look and see if this is browser unique, I don't seem to encounter this on Chrome. In fact I have the opposite problem, the search pre-fill is legible while my query is black on grey and quite difficult to read.

[bdice]

Interesting observation, the default input colors may differ by browser (I saw this in Firefox). Setting a color in the CSS should hopefully fix the problem for all browsers. 😊

edit: I think this change will apply to both the pre-filled “Search libcu++” and user input, in all browsers.

[harrism]

I definitely see the unreadable black on charcoal search box in Firefox. IMO we should get rid of the default black background website because it leads to usability issues. See also NVIDIA/cccl#942 .

[bdice]

Following up from the question about Chrome: I verified that this fix works for Firefox, Chrome, and Edge browsers. All three browsers show light text on a dark background in the placeholder text and when input is entered. Here's what it looks like when input is entered into the search box:

[wmaxey]

Thank you both for the feedback, I agree that the docs need a readability update, but at the moment that's somewhat beyond me. I'll take some time to find out if I can do it myself or bug Bryce about it.