Update extra.css

Set active link color to purple for better aesthetics.

Author: hsutaiyu

docs/_site_essentials/stylesheets/extra.css

@@ -135,6 +135,10 @@ div.main p {
 	box-shadow: none;
 }
 
+.md-nav__item .md-nav__link--active,
+.md-nav__item .md-nav__link--active code {
+  color:var(--purple) !important;
+}
 .md-sidebar__scrollwrap, .md-sidebar__inner, .md-nav--secondary, .md-nav__title {
 	box-shadow: none !important;
 	background-color: var(--smoke-white) !important;