[explore] remove grey background in standalone mode (#2503)

* [explore] remove grey background in standalone mode

* Going with background-transparent

superset/assets/javascripts/explorev2/components/ChartContainer.jsx

@@ -209,6 +209,8 @@ class ChartContainer extends React.PureComponent {
 
   render() {
     if (this.props.standalone) {
+      // dom manipulation hack to get rid of the boostrap theme's body background
+      $('body').addClass('background-transparent');
       return this.renderChart();
     }
     const queryResponse = this.props.queryResponse;

superset/assets/javascripts/explorev2/main.css

@@ -30,3 +30,7 @@
   margin-bottom: 0px;
   box-shadow: none;
 }
+
+.background-transparent {
+  background-color: transparent !important;
+}