fix(ObjectPage): contain stacking context within the page (#7756)

Author: Lukas742

packages/main/src/components/ObjectPage/ObjectPage.module.css

@@ -4,12 +4,14 @@
   --_ui5wcr_ObjectPage_title_fontsize: var(--sapObjectHeader_Title_FontSize);
 
   box-sizing: border-box;
+  position: relative;
+  /* Contain stacking context within the page */
+  z-index: 0;
   display: flex;
   flex-direction: column;
   width: 100%;
   height: 100%;
   max-height: 100vh;
-  position: relative;
   white-space: normal;
   font-family: var(--sapFontFamily);
   background-color: var(--sapBackgroundColor);