Stretch Widgets editor layout to full height

packages/edit-widgets/src/components/widget-areas-block-editor-content/style.scss

@@ -1,10 +1,27 @@
 .edit-widgets-block-editor {
 	position: relative;
-	background: $gray-100;
 
 	// This is the default font that is going to be used in the content of the areas (blocks).
 	font-family: $default-font;
 
+	// Block list needs to stretch to full screen height so blocks can
+	// be deselected when clicking outside widget areas.
+	display: flex;
+	flex-direction: column;
+	flex-grow: 1;
+
+	> div:last-of-type,
+	.block-editor-writing-flow,
+	.block-editor-writing-flow > div {
+		display: flex;
+		flex-direction: column;
+		flex-grow: 1;
+	}
+
+	.edit-widgets-main-block-list {
+		height: 100%;
+	}
+
 	// The button element easily inherits styles that are meant for the editor style.
 	// These rules enhance the specificity to reduce that inheritance.
 	// This is copied from edit-post/src/components/style.scss but without the padding.