Theres no specific entry for this menu, you'd be decreasing font size or whatever CSS property you're wanting. This version you're on is NOT mobile capable, v7.7 is.
Those elements would be
Custom Tags can be managed through the Custom Tags manager at:
Custom Tag Editor is located at CP -> Content Rebuilder -> Custom Tag Editor
As for the style editor the elements are broken down by page, this particular item is for the markup panel which has its own section "Markup Panel Properties" and the dropdown would be located as:
.markup_panel_popup
.markup_panel_unselect_text
.markup_panel_select_text