Simplify the font selection

Author: AA-Turner

doc/_themes/sphinx13/static/sphinx13.css

@@ -2,7 +2,7 @@
 
 /* Set master colours */
 :root {
-    --fonts-sans-serif: -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji";
+    --fonts-sans-serif: system-ui, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol", "Noto Color Emoji";
     --colour-sphinx-blue: #0A507A;
     --colour-text: #333;
     --colour-links-light: #057;