Change deemphasized text color in dark from gray-500 to gray-400

To show better contrast.

Google-Bug-Id: b/244303143
Release-Notes: skip
Change-Id: I6a7d9a13584076dbc38accfcd3866692a2fd850b

polygerrit-ui/app/styles/themes/dark-theme.ts

diff --git a/polygerrit-ui/app/styles/themes/dark-theme.ts b/polygerrit-ui/app/styles/themes/dark-theme.ts
index 3388aed..d11e372 100644
--- a/polygerrit-ui/app/styles/themes/dark-theme.ts
+++ b/polygerrit-ui/app/styles/themes/dark-theme.ts
@@ -101,7 +101,7 @@
     --primary-text-color: var(--gray-200);
     --link-color: var(--gerrit-blue-dark);
     --comment-text-color: var(--primary-text-color);
-    --deemphasized-text-color: var(--gray-500);
+    --deemphasized-text-color: var(--gray-400);
     --default-button-text-color: var(--gerrit-blue-dark);
     --chip-selected-text-color: var(--blue-100);
     --error-text-color: var(--red-200);