Fix missing search overlay in some themes like Rebalance (#40472)

* Set body opacity to 1 when instant search overlay is displayed

* changelog

* Update condition to execute only when opacity is 0

* Set opacity to 1 always when it has incorrect value

projects/packages/search/changelog/fix-missing-search-overlay-in-some-themes

@@ -0,0 +1,4 @@
+Significance: patch
+Type: fixed
+
+Fix missing instant search dialog for themes like Rebalance

projects/packages/search/src/instant-search/components/dom-event-handler.jsx

@@ -38,6 +38,7 @@ export default class DomEventHandler extends Component {
 		if ( this.props.isVisible !== prevProps.isVisible ) {
 			this.fixBodyScroll();
 		}
+		this.fixBodyOpacity();
 	}
 
 	disableUnnecessaryFormAndInputAttributes() {
@@ -190,6 +191,14 @@ export default class DomEventHandler extends Component {
 		}
 	};
 
+	fixBodyOpacity = () => {
+		if ( '1' !== document.body.style.opacity ) {
+			// This ensures the body is visible when the search dialog opens if
+			// the theme changes body opacity dynamically
+			document.body.style.opacity = '1';
+		}
+	};
+
 	/**
 	 * 1) When the overlay is open, we set body to fixed position.
 	 * 2) Body would be scrolled to top, so we need to set top to where the scroll position was.