Adding react scrollbar to the RHS thread (#2693)

* Adding scrollbar to the RHS thread

* Fixing the RHS thread scrolling issue

webapp/utils/utils.jsx

@@ -729,6 +729,7 @@ export function applyTheme(theme) {
         changeCss('::-webkit-scrollbar-thumb', 'background:' + changeOpacity(theme.centerChannelColor, 0.4), 1);
         changeCss('body', 'scrollbar-arrow-color:' + theme.centerChannelColor, 4);
         changeCss('.app__body .modal .about-modal .about-modal__logo svg, .app__body .post .post__img svg', 'fill:' + theme.centerChannelColor, 1);
+        changeCss('.app__body .scrollbar--horizontal, .app__body .scrollbar--vertical', 'background:' + changeOpacity(theme.centerChannelColor, 0.5), 2);
     }
 
     if (theme.newMessageSeparator) {