title: Substitute to ms-flex-preferred-size in CSS 4.0
body: <p>I'm completing training in remotely related subject but per course instructions I had to use Lumen bootstrap from bootswatch.com. I noticed that my site had problem displaying navigation bar. I traced the problem to css class that calls <code>-ms-flex-preferred-size</code>. Every occurance of that call is marked up by IDE as invalid in CSS 4.0. What should I substitute it for?</p>