Thanks @mboeni I later added text-align: left so it works for lengthy label

<q-tabs v-model="shownTab" vertical no-caps>
          <q-tab
            v-for="(dataRow, index) in data"
            :key="index"
            :name="'tab-'+index"
            style="justify-content:initial; text-align: left"
          >{{dataRow.label}}</q-tab>
</q-tabs>