Store primes in sessionStorage to make reloading the page quicker.

static/css/style.css

@@ -99,3 +99,12 @@
     bottom: 0;
     right: 0;
 }
+
+#remaining-reinforcements {
+    position: fixed;
+    bottom: 20px;
+    width: 100%;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+}