https://github.com/tracim/tracim/issues/729, add a margin-bottom on dropdownCreateBtn

frontend/src/css/Workspace.styl

     &__button
       display flex
       justify-content flex-end
-      margin 50px 15px 0 0
+      margin 45px 15px 45px 0
       width 100%
       &__btnaddworkspace
         margin-bottom 50px