koel/resources/assets/js/components/main-wrapper/index.vue

<template>
  <div id="mainWrapper">
    <sidebar></sidebar>
    <main-content></main-content>
    <extra></extra>
  </div>
</template>

<script>
import sidebar from './sidebar/index.vue';
import mainContent from './main-content/index.vue';
import extra from './extra/index.vue';

export default {
  components: { sidebar, mainContent, extra },
};
</script>

<style lang="sass">
@import "../../../sass/partials/_vars.scss";
@import "../../../sass/partials/_mixins.scss";

#mainWrapper {
  display: flex;
  flex: 1;
}
</style>