Fine-tune appearance of buttons in calling interface UI

GitLab: #97

Change-Id: Iecf16921171196547e2a392ba6826971ca23ac47
diff --git a/client/src/locale/en/translation.json b/client/src/locale/en/translation.json
index 049bc55..18bbf31 100644
--- a/client/src/locale/en/translation.json
+++ b/client/src/locale/en/translation.json
@@ -49,6 +49,7 @@
   "registration_success": "You've successfully registered! — Logging you in...",
 
   "share_screen": "Share your screen",
+  "share_window": "Share window",
   "share_screen_area": "Share an area of your screen",
   "share_file": "Share a file",