Nav item show garbled text when using local CSS

[pcplayer]

I have downloaded demo html from: https://github.com/picocss/examples/tree/master/v2-html.

It works fine on my computer.

And I have downloaded CSS to my computer, and if I modify the CSS link from:
href="https://cdn.jsdelivr.net/npm/@picocss/pico@2.0.6/css/pico.min.css”
to:
href="/css/pico.min.css“

and everything on the page is fine but the nav item of theme. When I drop it down, it show garbled text over the three options item text.
At the same time, I can change the theme by select the dark item.