fix(ui5-dialog): position block layer fixed (#1757)

Author: MapTo0

packages/main/src/themes/PopupStaticAreaStyles.css

@@ -1,6 +1,6 @@
 .ui5-block-layer {
 	display: none;
-	position: absolute;
+	position: fixed;
 	background-color: var(--sapBlockLayer_Background);
 	opacity: 0.6;
 	top: -500px;