revert changed md-admonition background color

was too bright for dark mode

Author: softhack007

docs/assets/stylesheets/extra.css

@@ -17,7 +17,7 @@
   --md-footer-bg-color: #1d1f21; /* discord link header and footer */
   --md-code-bg-color: #42464c;
   --md-code-fg-color: #FFF;
-  --md-admonition-bg-color: #3d4147;
+  --md-admonition-bg-color: #35383d;
   --md-admonition-fg-color: var(--md-default-fg-color);
   --md-typeset-table-color: #42464c;
   --md-code-hl-keyword-color: #a5d6ff;