[clang] [clang][dataflow] Show triangle in `<details>` element. (PR #67431)

[Sam McCall via cfe-commits]

================
@@ -122,10 +122,22 @@ code.line:has(.bb-select):before {
   font-size: x-small;
   flex-grow: 1;
 }
-.value summary {
+.value > summary {
   background-color: #ace;
   display: flex;
   justify-content: space-between;
+  cursor: pointer;
+}
+.value > summary::before {
+  content: '►';
+  margin-right: 0.5em;
+  font-size: 0.9em;
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sam-mccall wrote:

no accounting for taste I suppose :-)

https://github.com/llvm/llvm-project/pull/67431