[design] improve style guide tab index

Author: zombieFox

src/style-guide.html

@@ -50,7 +50,7 @@
     </div>
     <div class="input-wrap">
       <label for="radius" class="style-guide-control">Radius</label>
-      <input id="radius" class="style-guide-control radius" type="range" min="0" max="500" value="0" step="20" tabindex="-1">
+      <input id="radius" class="style-guide-control radius" type="range" min="0" max="500" value="0" step="20" tabindex="1">
     </div>
     <hr>
     <div class="button-wrap form-inline">