fix(website): hide hints dialog when closed

display:flex on <dialog> overrode the browser's implicit
display:none, causing the dialog to render inline at page bottom.
Scoped flex layout to [open] state.

Author: KristjanESPERANTO

website/index.css

@@ -413,6 +413,9 @@ main {
   color: var(--color-background);
   box-shadow: 0 8px 32px rgb(0 0 0 / 40%);
   overflow: hidden;
+}
+
+#hints-dialog[open] {
   display: flex;
   flex-direction: column;
 }