Hiho,
I am making my first Webix app with the pro version and having a difficulty replicating the bank demo app sidebar. I checked now always around but whatever i do it always adds fa- as prefix for the icons, while i can see it doesnt do that in the demo app. I assume there might be something off through the webix version, so far i try to keep it simple and replicate step by step on my own the bank demo, and so far all is good, beside this icon problem driving me crazy, so i could do " mdi mdi-school" and it works but with a “fa-” class in it 
if i do not make a space before it gets messed up. I do include the material design icons css. Here the sidebar view part:
{
view:“sidebar”,
css:theme,
width:200,
collapsed:(screen !== “wide”),
data:[
{ id:“courses”, value:(“Courses”), view:“icon”, icon:“mdi mdi-school” },
{ id:“reports”, value:(“Reports”), icon:" mdi mdi-monitor-dashboard" },
{ id:“demographics”, value:(“Demographics”), icon:" mdi mdi-account-box" },
{ id:“achievements”, value:(“Achievements”), icon:" mdi mdi-account-box" },
{ id:“account”, value:_(“Account”), icon:" mdi mdi-account-box" }
]
}