It looks like display: flex is pretty firmly placed in there.
I am guessing .visible-md-flex is a utility class, so I would NOT attempt to redeclare it as it may affect other elements throughout the site.
SOLUTION:
If you can remove the classes and then the a .hide class to the elements you want to hide .hide{ display:none;}
If you CAN’T edit the HTML, then you could increase the specificity of your selector until it works. Example: .container .toolbox .toolbox_share { display:none;}