port !1488 to vue3

src/components/settings_modal/settings_modal.vue

@@ -113,9 +113,9 @@
         <Checkbox :modelValue="!!expertLevel" @update:modelValue="expertLevel = Number($event)">
           {{ $t("settings.expert_mode") }}
         </Checkbox>
-        <portal-target
+        <span
           class="extra-content"
-          name="unscrolled-content"
+          id="unscrolled-content"
         />
       </div>
     </div>

src/components/settings_modal/tabs/theme_tab/theme_tab.vue

@@ -1018,9 +1018,9 @@
       </tab-switcher>
     </keep-alive>
 
-    <portal
+    <teleport
       v-if="isActive"
-      to="unscrolled-content"
+      to="#unscrolled-content"
     >
       <div class="apply-container">
         <button
@@ -1037,7 +1037,7 @@
           {{ $t('settings.style.switcher.reset') }}
         </button>
       </div>
-    </portal>
+    </teleport>
   </div>
 </template>
 

src/components/tab_switcher/tab_switcher.jsx

@@ -50,7 +50,7 @@ export default {
     activeIndex () {
       // In case of controlled component
       if (this.activeTab) {
-        return this.slots().findIndex(slot => this.activeTab === slot.key)
+        return this.slots().findIndex(slot => this.activeTab === slot.props.key)
       } else {
         return this.active
       }
@@ -58,7 +58,7 @@ export default {
     isActive () {
       return tabName => {
         const isWanted = slot => slot.props && slot.props['data-tab-name'] === tabName
-        return this.$slots.default.findIndex(isWanted) === this.activeIndex
+        return this.$slots.default().findIndex(isWanted) === this.activeIndex
       }
     },
     settingsModalVisible () {