minor fixes and docs

src/components/SidePane.jsx

@@ -214,6 +214,7 @@ export class SidePane extends Component {
 	}
 	dropHandler(e) {
 		e.preventDefault();
+		// Object with `children` key is to simulate a folder structure for root folder
 		this.props.onFileDrop(e.dataTransfer.getData('text/plain'), {
 			children: this.props.files
 		});

src/components/app.jsx

@@ -1283,9 +1283,17 @@ export default class App extends Component {
 		});
 	}
 
+	getRootClasses() {
+		const classes = [];
+		if (this.state.currentItem && this.state.currentItem.files) {
+			classes.push('is-file-mode');
+		}
+		return classes.join(' ');
+	}
+
 	render() {
 		return (
-			<div>
+			<div class={this.getRootClasses()}>
 				<div class="main-container">
 					<MainHeader
 						externalLibCount={this.state.externalLibCount}