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>