Make compatible with themes (#36)

Author: timja

src/main/frontend/pipeline-graph-view/pipeline-graph/main/support/labels.tsx

@@ -174,7 +174,7 @@ export function SequentialContainerLabel({
     maxWidth: sequentialStagesLabelOffset,
     overflow: "hidden",
     textOverflow: "ellipsis",
-    background: "white",
+    background: "var(--background, white)",
     padding: "0 7px",
     lineHeight: "1",
     whiteSpace: "nowrap",

src/main/frontend/pipeline-graph-view/pipeline-graph/styles/PipelineGraphWidget.scss

@@ -18,7 +18,6 @@
 }
 
 circle.halo {
-  stroke: white;
   fill: none;
 }