Switch to using message-box for the body and form elements in the UI of PDF.js. This will use the system's native UI font for each platform as well as fix the current inconsistency between the font of the text label for total page count and the text inside of the input element for current page number.

web/viewer.css

@@ -11,7 +11,12 @@ body {
   height: 100%;
   background-color: #404040;
   background-image: url(images/texture.png);
-  font-family: Segoe UI, Verdana, sans-serif;
+}
+
+body,
+input,
+select {
+  font-family: message-box;
 }
 
 .hidden {