AUT-3407: Include spinner Sass in application.scss

This is so that the styles for the spinner will be included
in the distributed CSS.

src/assets/scss/application.scss

@@ -25,6 +25,8 @@
 @import "components/warning-text/warning-text";
 
 @import "../../../node_modules/@govuk-one-login/frontend-language-toggle/stylesheet/styles";
+@import "prove-identity-callback/spinner";
+
 
 .interrupt-screen {
   background-color: #1d70b8;

src/assets/scss/prove-identity-callback/spinner.scss

@@ -0,0 +1,64 @@
+.spinner {
+  width: 80px;
+  height: 80px;
+  border-radius: 50%;
+  border-width: 12px;
+  border-style: solid;
+  border-color: #dee0e2;
+  border-top-color: #005ea5;
+  margin-bottom: govuk-spacing(3);
+
+  @media (forced-colors: active) {
+    forced-color-adjust: none;
+    border-top-color: transparent !important;
+  }
+
+  @media not (prefers-reduced-motion) {
+    -webkit-animation: spin 2s linear infinite;
+    animation: spin 2s linear infinite;
+  }
+
+  @media (prefers-reduced-motion) {
+    transform: rotate(0.125turn);
+  }
+
+  &__ready {
+    border-color: #005ea5;
+    -webkit-animation: none;
+    animation: none;
+  }
+}
+
+.spinner-container {
+  &__error {
+    .spinner,
+    .spinner-state-text {
+      display: none;
+    }
+  }
+}
+
+@-webkit-keyframes spin {
+  0% {
+    -webkit-transform: rotate(0deg);
+  }
+  100% {
+    -webkit-transform: rotate(360deg);
+  }
+}
+
+@keyframes spin {
+  0% {
+    transform: rotate(0deg);
+  }
+  100% {
+    transform: rotate(360deg);
+  }
+}
+
+.centre {
+  margin-left: auto;
+  margin-right: auto;
+  text-align: center;
+  display: block;
+}