https://snippet.dhtmlx.com/6ypy51mp
set title to red, but show black
Hi @jack.qiang 
Sometimes, when we use the css property is important to know the exactly structure. For example, in this case, title items wraps the text inside an span with the class .dhx_navbar-title--toolbar. This must works:
.aaa .dhx_navbar-title--toolbar {
color: red
}
Full example here
I hope the dev team never change this structure or this will cause some visual issues 
Without class name:
.aaa span {color: red}
Greetings