message: First screen: block the buttons until the app loads
  Add class for buttons and styles for buttons pseudo elements
  On branch newFirstScreen
  Changes to be committed:
  modified:   src/front/client/index.html
diff: transition: 0.15s;
  }
  + .starter-modal__btn.app-not-load {
  + position: relative;
  + pointer-events: none;
  + }
  +
  + .starter-modal__btn.app-not-load::before {
  + content: "";
  + position: absolute;
  + top: 0;
  + left: 0;
  + width: 100%;
  + height: 100%;
  + border-radius: inherit;
  + background-color: #6144e5;
  + }
  +
  + .starter-modal__btn.app-not-load::after {
  + content: "";
  + position: absolute;
  + top: 50%;
  + left: 50%;
  + transform: translate(-50%, -50%);
  + width: 2em;
  + height: 2em;
  + border-radius: 50%;
  + background-color: #fff;
  + animation: spin 1s infinite;
  + }
  +
  + @keyframes spin {
  + 0% {
  + transform: translate(-50%, -50%) scale(0);
  + opacity: 1;
  + }
  + 100% {
  + transform: translate(-50%, -50%) scale(1);
  + opacity: 0;
  + }
  + }
  +
  .starter-modal__btn:hover {
  background-color: #9785ed;
  }
  </div>
  <div class="starter-modal__btn-container">
  - <button class="starter-modal__btn starter-modal__btn_create-wallet">
  + <button class="starter-modal__btn starter-modal__btn_create-wallet app-not-load">
  Create Wallet
  </button>
  - <button class="starter-modal__btn starter-modal__btn_connect-wallet">
  + <button class="starter-modal__btn starter-modal__btn_connect-wallet app-not-load">
  <?xml version="1.0" encoding="utf-8"?>
  <svg version="1.1"
  xmlns="http://www.w3.org/2000/svg" x="0px" y="0px" viewBox="0 0 318.6 318.6">
  </svg>
  Connect Wallet
  </button>
  - <button class="starter-modal__btn starter-modal__btn_skip">
  + <button class="starter-modal__btn starter-modal__btn_skip app-not-load">
  Skip
  </button>
  </div>
  <!-- /Loader before any JS -->
  <!-- This library using in React componet (WallerSlider) -->
  - <script src="https://cdnjs.cloudflare.com/ajax/libs/Swiper/4.5.1/js/swiper.min.js"
  + <script defer src="https://cdnjs.cloudflare.com/ajax/libs/Swiper/4.5.1/js/swiper.min.js"
  integrity="sha256-4sETKhh3aSyi6NRiA+qunPaTawqSMDQca/xLWu27Hg4=" crossorigin="anonymous"></script>
  <!-- Start Modal Scripts -->
  </script>
  <script>
  + window.onload = () => {
  + document.querySelectorAll('.starter-modal__btn').forEach(btn => {
  + btn.classList.remove('app-not-load');
  + })
  + }
  +
  const btnCreateWallet = document.querySelector(
  '.starter-modal__btn_create-wallet'
  );
  