content/static: adjust dark theme accented icon filter

The accented icon filter is adjusted to match the
color of links.

Change-Id: I980c7a423c4107d4fe9ff541c50a55f27344203e
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/326351
Trust: Jamal Carvalho <jamal@golang.org>
Run-TryBot: Jamal Carvalho <jamal@golang.org>
Reviewed-by: Jonathan Amsterdam <jba@google.com>

content/static/_icon/icon.css

@@ -21,3 +21,7 @@
   filter: brightness(0) saturate(100%) invert(100%) sepia(97%) saturate(13%) hue-rotate(245deg)
     brightness(103%) contrast(107%);
 }
+[data-theme='dark'] .go-Icon--accented {
+  filter: brightness(0) invert(57%) sepia(63%) saturate(4864%) hue-rotate(160deg) brightness(100%)
+    contrast(101%);
+}