bump up height of progress bars, give some extra depth with stacking bars, and then make the stacked bars actually work

less/progress-bars.less

@@ -44,8 +44,8 @@
 // Outer container
 .progress {
   overflow: hidden;
-  height: 18px;
-  margin-bottom: 18px;
+  height: @baseLineHeight;
+  margin-bottom: @baseLineHeight;
   #gradient > .vertical(#f5f5f5, #f9f9f9);
   .box-shadow(inset 0 1px 2px rgba(0,0,0,.1));
   .border-radius(4px);
@@ -65,6 +65,9 @@
   .box-sizing(border-box);
   .transition(width .6s ease);
 }
+.progress .bar + .bar {
+  .box-shadow(~"inset 1px 0 0 rgba(0,0,0,.15), inset 0 -1px 0 rgba(0,0,0,.15)");
+}
 
 // Striped bars
 .progress-striped .bar {