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/overview/Overview.vue

@@ -200,7 +200,7 @@ const handleDownloadLogfile = () => {
     <template #actions>
       <VButton size="sm" @click="handleCopy">
         <template #icon>
-          <IconClipboardLine class="h-full w-full" />
+          <IconClipboardLine />
         </template>
         {{ $t("core.common.buttons.copy") }}
       </VButton>