refactor: update dialog custom CSS properties fallback values (#10199)

Author: web-padawan

packages/dialog/src/styles/vaadin-dialog-overlay-base-styles.js

@@ -29,10 +29,10 @@ export const dialogOverlayBase = css`
   }
 
   [part='overlay'] {
-    background: var(--vaadin-dialog-background, var(--vaadin-background-color));
+    background: var(--vaadin-dialog-background, var(--vaadin-overlay-background, var(--vaadin-background-color)));
     background-origin: border-box;
-    border: var(--vaadin-dialog-border-width, 1px) solid
-      var(--vaadin-dialog-border-color, var(--vaadin-border-color-secondary));
+    border: var(--vaadin-dialog-border-width, var(--vaadin-overlay-border-width, 1px)) solid
+      var(--vaadin-dialog-border-color, var(--vaadin-overlay-border-color, var(--vaadin-border-color-secondary)));
     box-shadow: var(--vaadin-dialog-box-shadow, 0 8px 24px -4px rgba(0, 0, 0, 0.3));
     border-radius: var(--vaadin-dialog-border-radius, var(--vaadin-radius-l));
     width: max-content;