Vertical menu for Vaadin Bakery App

Flow
31

I noticed one thing.
If I change

body {
height: 100vh;
width: 100vw;
overflow: hidden;
margin: 0;

}

instead of the default

body {
     height: 100vh;
     width: 100vw;
     margin: 0;
}

everything works well.
But how can the body’s css be modified? Is this the right approach?