Refactor code structure for improved readability and maintainability

Fuchs/wwwroot/web/fis.inv.css

@@ -96,6 +96,14 @@ table.if td.num {
   margin: 0.2rem 0;
 }
 
+@keyframes fis_spin {
+  from {
+    transform: rotate(0deg);
+  }
+  to {
+    transform: rotate(360deg);
+  }
+}
 .edit_frm .invoice_layout {
   margin: 2rem 2rem 2rem auto; /* align right */
   width: 50rem;
@@ -381,6 +389,21 @@ table.if td.num {
 .edit_frm .invoice_layout.freeze::before tr:hover > td.aux > .axf {
   display: inline-flex;
 }
+.edit_frm .invoice_layout.freeze::after {
+  content: "";
+  position: absolute;
+  top: 50%;
+  left: 50%;
+  width: 3rem;
+  height: 3rem;
+  margin: -1.5rem 0 0 -1.5rem;
+  border: 0.4rem solid rgba(255, 255, 255, 0.35);
+  border-top-color: #FFF;
+  border-radius: 50%;
+  z-index: 11;
+  pointer-events: none;
+  animation: fis_spin 0.8s linear infinite;
+}
 
 .modal-body .lstfrm {
   display: block;