compose: Allow left arrow to scroll buttons.

web/src/compose_state.ts

@@ -148,6 +148,15 @@ function cursor_at_start_of_whitespace_in_compose(): boolean {
     return message_content() === "" && cursor_position === 0;
 }
 
+export function focus_in_formatting_buttons(): boolean {
+    const is_focused_formatting_button =
+        document.activeElement?.classList.contains("compose_control_button");
+    if (is_focused_formatting_button) {
+        return true;
+    }
+    return false;
+}
+
 export function focus_in_empty_compose(
     consider_start_of_whitespace_message_empty = false,
 ): boolean {

web/src/hotkey.js

@@ -936,6 +936,9 @@ export function process_hotkey(e, hotkey) {
         } else if (overlays.streams_open()) {
             stream_settings_ui.toggle_view(event_name);
             return true;
+        } else if (compose_state.focus_in_formatting_buttons()) {
+            // Allow left arrow to scroll the formatting buttons backward
+            return false;
         }
 
         message_edit.edit_last_sent_message();