Position "or" vertical aligned.

dist/semantic.css

@@ -1603,7 +1603,8 @@ a:hover {
   margin-left: -0.892855em;
   width: 1.78571em;
   height: 1.78571em;
-  line-height: 1.58571em;
+  vertical-align: middle;
+  line-height: 1.78571em;
   color: rgba(0, 0, 0, 0.4);
   font-style: normal;
   font-weight: bold;

src/definitions/elements/button.less

@@ -891,6 +891,7 @@
   width: @orCircleSize;
   height: @orCircleSize;
 
+  vertical-align: middle;
   line-height: @orLineHeight;
   color: @orTextColor;
 

src/themes/default/elements/button.variables

@@ -133,7 +133,7 @@
 
 @orCircleDistanceToEdge: (@verticalPadding);
 @orCircleSize: @orHeight - @orCircleDistanceToEdge;
-@orLineHeight: (@orCircleSize - 0.2em);
+@orLineHeight: (@orCircleSize);
 @orBoxShadow: @borderBoxShadow;
 
 @orVerticalOffset: -(@orCircleSize / 2);