Properly center and space end screen

This patch fixes the issue that the text and the check mark icon of the
end screen is pushed to the top of the end space with basically no
spacing. This is caused by an incorrect CSS calculation.

src/main/TheEnd.tsx

@@ -34,7 +34,7 @@ const TheEnd: React.FC = () => {
 
   const theEndStyle = css({
     width: "100%",
-    height: "calc(100% - 64px)",
+    height: "calc(100vh - 64px)",
     display: "flex",
     flexDirection: "column",
     justifyContent: "center",