make footer expand to fill empty vertical space

style.css

@@ -21,6 +21,16 @@ Use it to make something cool, have fun, and share what you've learned
 with others.
 */
 
+html, body {
+  height: 100%;
+}
+
+.wp-site-blocks{
+  display: flex;
+  flex-direction: column;
+  height: 100%;
+}
+
 .wp-site-blocks h2 {
   display: flex;
   height: 36px;
@@ -69,4 +79,12 @@ with others.
   margin-bottom: -90px;
   z-index: -20;
   position: relative;
+}
+
+.wp-site-blocks footer {
+  flex-grow: 1;
+}
+
+.wp-site-blocks .footer {
+  height: 100%;
 }