add default theme

resources/admin_themes/custom/scss/bootstrap/mixins/_nav-divider.scss

@@ -0,0 +1,10 @@
+// Horizontal dividers
+//
+// Dividers (basically an hr) within dropdowns and nav lists
+
+@mixin nav-divider($color: $nav-divider-color, $margin-y: $nav-divider-margin-y) {
+  height: 0;
+  margin: $margin-y 0;
+  overflow: hidden;
+  border-top: 1px solid $color;
+}