File overlays now show a blurred representation of the file in the background.

src/web/stylesheets/layout/_io.css

@@ -84,10 +84,17 @@
     top: 0;
     width: 100%;
     height: 100%;
-    background-color: var(--title-background-colour);
     display: none;
 }
 
+.file-overlay {
+    position: absolute;
+    opacity: 0.8;
+    background-color: var(--title-background-colour);
+    width: 100%;
+    height: 100%;
+}
+
 #show-file-overlay {
     position: absolute;
     right: 15px;