vaadin 7: CSS of a HeaderRow with a Filter

I added a TextField with a StringFilter to a Grid, just like the example says []

but the filter doesn’t have a good margin at bottom, how can I fix this? I don’t know anything about CSS, I would appreciate a hand

Update: partial solution from a colleague

    .v-grid-header .v-grid-row .v-grid-cell .v-textfield {
        height: $v-font-size*2 !important;
        margin-bottom: 2px;