A11y tweaks to the left pane and timeline

ts/components/LeftPane.tsx

@@ -601,7 +601,7 @@ export function LeftPane({
   }
 
   return (
-    <div
+    <nav
       className={classNames(
         'module-left-pane',
         isResizing && 'module-left-pane--is-resizing',
@@ -706,7 +706,7 @@ export function LeftPane({
           },
         })}
       {crashReportCount > 0 && renderCrashReportDialog()}
-    </div>
+    </nav>
   );
 }
 

ts/components/conversation/LastSeenIndicator.tsx

@@ -19,8 +19,14 @@ export const LastSeenIndicator = forwardRef<HTMLDivElement, Props>(
 
     return (
       <div className="module-last-seen-indicator" ref={ref}>
-        <div className="module-last-seen-indicator__bar" />
+        <div className="module-last-seen-indicator__bar" role="separator" />
-        <div className="module-last-seen-indicator__text">{message}</div>
+        <div
+          aria-level={6}
+          className="module-last-seen-indicator__text"
+          role="heading"
+        >
+          {message}
+        </div>
       </div>
     );
   }

ts/components/conversation/Timeline.tsx

@@ -871,6 +871,7 @@ export class Timeline extends React.Component<
           key={messageId}
           data-item-index={itemIndex}
           data-message-id={messageId}
+          role="listitem"
         >
           <ErrorBoundary i18n={i18n} showDebugLog={showDebugLog}>
             {renderItem({
@@ -1047,7 +1048,7 @@ export class Timeline extends React.Component<
 
               {floatingHeader}
 
-              <div
+              <main
                 className="module-timeline__messages__container"
                 onScroll={this.onScroll}
                 ref={this.containerRef}
@@ -1059,6 +1060,7 @@ export class Timeline extends React.Component<
                     haveOldest && 'module-timeline__messages--have-oldest'
                   )}
                   ref={this.messagesRef}
+                  role="list"
                 >
                   {haveOldest && (
                     <>
@@ -1079,7 +1081,7 @@ export class Timeline extends React.Component<
                     style={AT_BOTTOM_DETECTOR_STYLE}
                   />
                 </div>
-              </div>
+              </main>
 
               {shouldShowScrollDownButton ? (
                 <ScrollDownButton