Adjust welcome overlay positioning for larger viewports

src/lib/overlays/welcome.svelte

@@ -59,11 +59,12 @@
 <style>
   #popup {
     position: fixed;
-    top: 50%;
+    top: 50px;
     left: 50%;
-    transform: translateY(-50%) translateX(-50%);
+    transform: translateX(-50%);
     width: 85%;
     height: 85vh;
+    max-height: 600px;
     overflow-y: auto;
     max-width: 400px;
     margin: auto;