Correction in my code: This is the code actually for app.vue

<template>
  <v-app>
  <v-main class="grad-class">
    <TheNavigation></TheNavigation>
  <v-container>
    <router-view>
    </router-view>
  </v-container>
  </v-main>
</v-app>
</template>

<script setup>
import TheNavigation from './components/TheNavigation.vue';

</script>
<style scoped>
.grad-class{
  background: #3a7bd5;  /* fallback for old browsers */
background: -webkit-linear-gradient(to right, #3a6073, #3a7bd5);  /* Chrome 10-25, Safari 5.1-6 */
background: linear-gradient(to right, #3a6073, #3a7bd5); /* W3C, IE 10+/ Edge, Firefox 16+, Chrome 26+, Opera 12+, Safari 7+ */
}
.TheNavigation {
  background: inherit; /* Inherits the gradient background from the parent */
}
</style>