Add focus animation to back button

src/client/lazy-app/Compress/style.css

@@ -113,6 +113,13 @@
 
   & > svg {
     width: 47px;
+    overflow: visible;
+  }
+
+  &:focus .back-blob {
+    stroke: var(--deep-blue);
+    stroke-width: 5px;
+    animation: strokePulse 500ms ease forwards;
   }
 
   @media (min-width: 600px) {
@@ -124,6 +131,15 @@
   }
 }
 
+@keyframes strokePulse {
+  from {
+    stroke-width: 8px;
+  }
+  to {
+    stroke-width: 5px;
+  }
+}
+
 .back-blob {
   fill: var(--hot-pink);
   opacity: 0.77;