rollback plex-sans since the feedback from the user wasn't ok (inter was still 'fuzzy')

ui/src/css/base.css

@@ -133,6 +133,9 @@ body {
     color: var(--surfaceTxtColor);
     background: var(--surfaceColor);
     height: 100%;
+
+    /* normalizes IBM Plex Sans font rendering between Chrome and Firefox */
+    letter-spacing: 0.004em;
 }
 
 h1,