Change the styling of the <DependencyGraph> to have more contrast in light mode

Signed-off-by: Oliver Sand <oliver.sand@sda-se.com>

.changeset/brave-eggs-rush.md

@@ -0,0 +1,6 @@
+---
+'@backstage/core-components': patch
+---
+
+Change the styling of the `<DependencyGraph>` to have more contrast in light
+mode. Nodes now have a design similar to material UI buttons.

packages/core-components/src/components/DependencyGraph/DefaultNode.tsx

@@ -21,11 +21,11 @@ import { RenderNodeProps } from './types';
 
 const useStyles = makeStyles((theme: BackstageTheme) => ({
   node: {
-    fill: theme.palette.background.paper,
-    stroke: theme.palette.border,
+    fill: theme.palette.primary.light,
+    stroke: theme.palette.primary.light,
   },
   text: {
-    fill: theme.palette.textContrast,
+    fill: theme.palette.primary.contrastText,
   },
 }));