Add default font-size and line-height styles.

Redeclare default font-size using ems (equates to 16px if user
has not altered their prefs). Set a common line-height value to
improve readability in most cases. Should keep people happy.

Ref h5bp#723
Close h5bp#825

css/style.css

@@ -33,7 +33,7 @@ audio:not([controls]) { display: none; }
 
 html { font-size: 100%; overflow-y: scroll; -webkit-text-size-adjust: 100%; -ms-text-size-adjust: 100%; }
 
-body { margin: 0; /* add your base font-size and line-height here */ }
+body { margin: 0; font-size: 1em; line-height: 1.4; }
 
 body, button, input, select, textarea { font-family: sans-serif; color: #222; }