Main menu separator for specific menu items?

Good afternoon,

We have applied the following CSS below to adding padding to the left of our main menu ‘login’ and register’ links. We also wish to add a ‘/’ in between these menu items (not the entire menu) however this appears to not be working. Please could you offer advice?

#menu-item-243{
padding-left: 40px;
}

ul#avia-menu > #menu-item-243 > li > a:after{
content: ‘/’;
display: inline-block;
position: relative;
left: 13px;
}

Many thanks