remove text indent on carets (not needed) and add inline replacement mixin

less/buttons.less

@@ -8,6 +8,7 @@
 // Core
 .btn {
   display: inline-block;
+  .ie7-inline-block();
   padding: 4px 10px 4px;
   margin-bottom: 0; // For input.btn
   font-size: @baseFontSize;

less/mixins.less

@@ -98,7 +98,14 @@
   white-space: nowrap;
 }
 
-
+// New image replacement
+// -------------------------
+// Source: http://www.zeldman.com/2012/03/01/replacing-the-9999px-hack-new-image-replacement/
+.hide-text {
+  overflow: hidden;
+  text-indent: 100%;
+  white-space: nowrap;
+}
 
 // FONTS
 // --------------------------------------------------