<v-app-bar v-if="$vuetify.breakpoint.xsOnly" app/>
$vuetify.breakpoint.xsOnly =xs사이즈일때만 보여준다.
<v-card-title>
$vuetify.breakpoint.name ={{ $vuetify.breakpoint.name}}
</v-card-title>
$vuetify.breakpoint.name ={{ $vuetify.breakpoint.name}}
= 현시점 브레이크 포인트