Added background animation to habe a little bit more interesting page

src/styles.scss

@@ -407,9 +407,15 @@ app-root {
   min-height: 100vh;
 }
 
+.app-container {
+  width: 100%;
+  max-width: var(--app-maxWidth);
+  margin: 1rem auto;
+
+}
+
 .app-surface {
   flex-grow: 1;
-  background: var(--app-bg);
   color: var(--app-fg);
   transition: background-color 220ms ease, color 220ms ease;
 }