Adding custom-theme scss used for custom-theme example. Added ability to set a hover scale size in the theme which will scale the X and Y rails when hovered.

examples/custom-theme.scss

@@ -0,0 +1,12 @@
+@import '../src/css/main';
+
+.ps-theme-custom-theme {
+  @include ps-container(map-merge($ps-theme-default, (
+          border-radius: 0,
+          scrollbar-x-rail-height: 20px,
+          scrollbar-x-height: 20px,
+          scrollbar-y-rail-width: 20px,
+          scrollbar-y-width: 20px,
+          scrollbar-rail-scale-hover: 1.5
+  )));
+}