Use new button variants

src/components/StickerPickerBottomSheet.vue

@@ -13,7 +13,7 @@
     </v-tabs>
     <v-tabs-window v-model="currentStickerPack">
       <v-window-item v-for="(pack,ipack) in packs" :key="'pack-content-' + ipack" :value="'pack-' + ipack">
-        <v-card flat>
+        <v-card variant="flat">
           <v-container fluid>
             <v-row>
               <v-col cols="2" v-for="sticker in stickersInPack(pack)" :key="pack + sticker.name">