refactor: improve button component styles (#7517)

#### What type of PR is this?

/area ui
/kind improvement
/milestone 2.21.x

#### What this PR does / why we need it:

1. Add ghost variant
2. Improve icon style
3. Refactoring css using scss functions

#### Does this PR introduce a user-facing change?

```release-note
None
```

ui/console-src/modules/system/backup/Backups.vue

@@ -68,7 +68,7 @@ onMounted(async () => {
     <template #actions>
       <VButton type="secondary" @click="handleCreate">
         <template #icon>
-          <IconAddCircle class="h-full w-full" />
+          <IconAddCircle />
         </template>
         {{ $t("core.backup.operations.create.button") }}
       </VButton>