fix: ensure class def color is applied to edge label

on-behalf-of: @Mermaid-Chart <hello@mermaidchart.com>

cypress/integration/rendering/flowchart-v2.spec.js

@@ -1133,4 +1133,17 @@ end
       `
     );
   });
+
+  it('V2 - 17: should apply class def colour to edge label', () => {
+    imgSnapshotTest(
+      ` graph LR
+    id1(Start) link@-- "Label" -->id2(Stop)
+    style id1 fill:#f9f,stroke:#333,stroke-width:4px
+
+class id2 myClass
+classDef myClass fill:#bbf,stroke:#f66,stroke-width:2px,color:white,stroke-dasharray: 5 5
+class link myClass
+`
+    );
+  });
 });

packages/mermaid/src/rendering-util/rendering-elements/edges.js

@@ -25,7 +25,7 @@ import {
 import rough from 'roughjs';
 import createLabel from './createLabel.js';
 import { addEdgeMarkers } from './edgeMarker.ts';
-import { isLabelStyle } from './shapes/handDrawnShapeStyles.js';
+import { isLabelStyle, styles2String } from './shapes/handDrawnShapeStyles.js';
 
 const edgeLabels = new Map();
 const terminalLabels = new Map();
@@ -43,8 +43,10 @@ export const getLabelStyles = (styleArray) => {
 export const insertEdgeLabel = async (elem, edge) => {
   let useHtmlLabels = evaluate(getConfig().flowchart.htmlLabels);
 
+  const { labelStyles } = styles2String(edge);
+  edge.labelStyle = labelStyles;
   const labelElement = await createText(elem, edge.label, {
-    style: getLabelStyles(edge.labelStyle),
+    style: edge.labelStyle,
     useHtmlLabels,
     addSvgBackground: true,
     isNode: false,