Add File Browser Styling (#4085)

Use CSS to style the selected and hovered items in the File Browser

data/themes/default/style.css

@@ -7,6 +7,28 @@ QLabel, QTreeWidget, QListWidget, QGroupBox, QMenuBar {
 	color: #d1d8e4;
 }
 
+QTreeView {
+	outline: none;
+}
+
+QTreeWidget::item:hover,
+QTreeWidget::branch:hover {
+	background-color: #3C444E;
+}
+
+QTreeWidget::item:selected,
+QTreeWidget::branch:selected {
+	background-color: #17793b;
+}
+
+QTreeView::branch:has-children:open {
+	border-image: url("resources:open_branch.png") 0;
+}
+
+QTreeView::branch:has-children:closed {
+	border-image: url("resources:closed_branch.png") 0;
+}
+
 QMdiArea {
 	background-color: #111314;
 }