Vue

HTML

<script src="https://unpkg.com/vue-select@latest"></script>
<link rel="stylesheet" href="https://unpkg.com/vue-select@latest/dist/vue-select.css">
<script src="https://cdnjs.cloudflare.com/ajax/libs/axios/0.19.2/axios.min.js"></script>
<div id="app">
  <v-select :options="options" 
   v-model="someVar">
   </v-select>
</div>

SCSS

.vs__dropdown-option--selected {
  background-color: red  !important;
}

Vue

Vue.component('v-select', VueSelect.VueSelect)

new Vue({
  el: "#app",
  data: {
	someVar: "baz",
	options: [
      'foo',
      'bar',
      'baz'
    ]
	}
})