webapp: optimize body bottom padding and length

long forms, when scrolled to the bottom, would leave no space between
the bottom of the viewport and the buttons, which is unpleasent.

short views would still createa large (high) body, for apparently no
reason.

webapp/src/App.vue

@@ -18,7 +18,7 @@ export default defineComponent({
 <style>
 /* Show it is fixed to the top */
 body {
-    min-height: 75rem;
+    padding-bottom: 1rem;
     padding-top: 4.5rem;
 }
 </style>