Add error indicator when the devtools are collapsed

Author: marthacryan

dash/dash-renderer/src/components/error/menu/DebugMenu.css

@@ -164,7 +164,15 @@
 .dash-debug-menu__toggle--expanded {
     transform: rotate(180deg);
 }
-
+.dash-debug-menu__error-indicator {
+    width: 8px;
+    height: 8px;
+    background-color: red;
+    border-radius: 100%;
+    position: absolute;
+    right: 3px;
+    top: 13px;
+}
 .dash-debug-menu__status {
     display: flex;
     align-items: center;

dash/dash-renderer/src/components/error/menu/DebugMenu.react.js

@@ -165,6 +165,9 @@ const DebugMenu = ({error, hotReload, config, children}) => {
                     )}
                 >
                     <Expand />
+                    {errCount > 0 && collapsed ? (
+                        <div className='dash-debug-menu__error-indicator' />
+                    ) : null}
                 </button>
             </div>
             {children}