Hide Add icon

Hi,

I would like the "Add" icon to become invisible. 

When I set in a Formula field the following instruction :

html("<style>div.i-setting-add{display:none}</style>")

then the icon disappears.

When I put the text null in “Display field only, if”, this no longer works and the Add icon becomes visible again.

I might be doing something wrong!

Tx

Regards

Michel