Apply Next recommandation

pages/_app.jsx

@@ -4,6 +4,7 @@ import React from "react";
 import { Provider } from "react-redux";
 
 import makeApplicationState from "../redux/make-application-state";
+import "../styles/styles.scss";
 
 class LexImpactApplicationWrapper extends App {
   render() {

pages/index.jsx

@@ -16,7 +16,6 @@ import withRoot from "../lib/withRoot";
 import {
   disabledEtat, fetchSimPop, showAddCasTypesPopin, simulateCasTypes,
 } from "../redux/actions";
-import "../styles/index.scss";
 
 const mapStateToProps = ({ token }) => ({
   isUserLogged: !!token,

styles/index.scss

-@import './variables';
-
-:global {
-
-  html {
-    background-image: url(../static/images/tramebackground.png);
-  }
-
-  input.mui-number-stepper::-webkit-inner-spin-button,
-  input.mui-number-stepper::-webkit-outer-spin-button {
-    -webkit-appearance: none;
-    margin: 0;
-  }
-
-}

styles/styles.scss

+html {
+  background-image: url(../static/images/tramebackground.png);
+}