CIP #57952 improve edition background

public/admin/skins/bokeh74/colors.css

@@ -38,4 +38,6 @@
 
     --help-link: #6FCFFF;
     --help-link-highlight: #6FBFFF;
+
+    --edition-background: rgba(255, 255, 0, 0.5);
 }

public/admin/skins/bokeh74/form.css

@@ -89,12 +89,14 @@
     height: 100%;
     width: 100%;
     position: absolute;
-    background: var(--line-highlight);
+    background: var(--edition-background);
     background-position: center;
     background-repeat: no-repeat;
     z-index: 100;
     display: block;
     top: 0;
+    left: 0;
+    filter: blur(2px);
 }
 
 .admin-form #liste_picto_picto td {