change .span* inputs to use content-sizing: border-box; to make them behave as block level elements

less/responsive.less

@@ -33,6 +33,26 @@
     line-height: @baseLineHeight;
   }
 
+  // Make span* classes full width
+  input[class*="span"],
+  select[class*="span"],
+  textarea[class*="span"],
+  .uneditable-input {
+    display: block;
+    width: 100%;
+    height: 28px; /* Make inputs at least the height of their button counterpart */
+    /* Makes inputs behave like true block-level elements */
+    -webkit-box-sizing: border-box; /* Older Webkit */
+       -moz-box-sizing: border-box; /* Older FF */
+        -ms-box-sizing: border-box; /* IE8 */
+            box-sizing: border-box; /* CSS3 spec*/
+  }
+  // But don't let it screw up prepend/append inputs
+  .input-prepend input[class*="span"],
+  .input-append input[class*="span"] {
+    width: auto;
+  }
+
   // Update checkboxes for iOS
   input[type="checkbox"],
   input[type="radio"] {