fixed a spelling error

src/main/resources/css/dark_theme.css

@@ -939,11 +939,11 @@
 
 /*******************************************************************************
  *                                                                             *
- * Add box                                                                   *
+ * Ad box                                                                   *
  *                                                                             *
  ******************************************************************************/
 
-.add-box {
+.ad-box {
 	-fx-padding: 12px;
 	-fx-background-color: CONTROL_BORDER_NORMAL, CONTROL_BG_NORMAL;
 	-fx-background-insets: 0, 1px;

src/main/resources/css/light_theme.css

@@ -938,11 +938,11 @@
 
 /*******************************************************************************
  *                                                                             *
- * Add box                                                                   *
+ * Ad box                                                                   *
  *                                                                             *
  ******************************************************************************/
 
-.add-box {
+.ad-box {
 	-fx-padding: 12px;
 	-fx-background-color: CONTROL_BORDER_NORMAL, CONTROL_BG_NORMAL;
 	-fx-background-insets: 0, 1px;

src/main/resources/fxml/share_vault.fxml

@@ -75,7 +75,7 @@
 				<Label text="%shareVault.remarkBestPractices" wrapText="true"/>
 			</HBox>
 			<Region minHeight="12"/>
-			<HBox alignment="CENTER_LEFT" spacing="6" styleClass="add-box">
+			<HBox alignment="CENTER_LEFT" spacing="6" styleClass="ad-box">
 				<VBox spacing="6" alignment="CENTER_LEFT">
 					<ImageView HBox.hgrow="ALWAYS" fitWidth="180" preserveRatio="true" cache="true">
 						<Image url="@../img/hub_logo.png"/>