x/pkgsite: deprecation background color is too bright on dark mode

[mvdan]

Take a look at how https://pkg.go.dev/path/filepath#HasPrefix looks on the light theme:

And now the dark theme:

The yellow color changes, and I think the intent was to make it darker for the dark theme. But instead, we simply get a far more striking yellow, that's nearly as bright as the light theme's.

On one hand, I find the black text much harder to read on the dark theme - the stronger yellow background distracts my eyes.

On the other hand, the stronger yellow seems to go against the purpose of the dark theme - to be easy on the eyes and not be too bright. If I open that page on the dark theme in a dark room, the yellow stands out significantly, and can easily light up my entire face yellow :)

For example, using my amazing non-existent design skills, here's how it looks if I keep the text color following the theme, and change the dark warning background to be a darker yellow color, #906e00:

I'm sure it looks horrible to anyone with UI skills, but at least it looks more like a readable dark theme to me :)

cc @julieqiu

[mvdan]

I tried to go for even darker yellows, closer to either gray or black, but they started looking more like brown or weird greens, so I don't know if that can fly.

In any case, I want the color to not jump out as much, just like it doesn't in the light theme.

[julieqiu]

/cc @jinhongy @jamalc

[gopherbot]

Change https://golang.org/cl/355190 mentions this issue: static: improve dark mode UI

[jamalc]

The recommendation we're getting from UX is just a reduction in saturation. It looks fine to me. Any objections?

[mvdan]

@jamalc that looks significantly better than what we have now indeed :) And certainly prettier than the color I came up with.