use variables for progress bar

src/client/styles/scss/_override-bootstrap-variables.scss

@@ -97,3 +97,9 @@ $input-bg-disabled:              $btn-default-bgcolor;
 
 //** `<input>` border color
 $input-border:                   $border;
+
+//== Progress bar
+$progress-height: 4px;
+$progress-border-radius: 0;
+$progress-bg: #f0f0f0;
+$progress-box-shadow: none;

src/client/styles/scss/_override-bootstrap.scss

@@ -130,3 +130,9 @@ fieldset[disabled] .btn {
     box-shadow: none;
   }
 }
+
+// progress bar
+.progress {
+  margin-bottom: 18px;
+  overflow: hidden;
+}

src/client/styles/scss/theme/_apply-colors.scss

@@ -152,18 +152,6 @@ legend {
   }
 }
 
-/*
- * progress bar
- */
-.progress {
-  height: 4px;
-  margin-bottom: 18px;
-  overflow: hidden;
-  background-color: #f0f0f0;
-  border-radius: 0;
-  box-shadow: none !important;
-}
-
 /*
  * cards
  */