Migrator: Add preliminary styles to stack trace

Change-Id: Iac8fdccb18b5ba04b058236ac1ee9b60643f67cf
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/138924
Reviewed-by: Paul Berry <paulberry@google.com>
Commit-Queue: Samuel Rawlins <srawlins@google.com>

Author: srawlins

pkg/analysis_server/lib/src/edit/nnbd_migration/resources/migration.css

@@ -356,6 +356,31 @@ footer .wide {
   cursor: pointer;
 }
 
+p.trace .type-description {
+  /* From HLJS's .hljs-keyword, .hljs-selector-tag, .hljs-deletion */
+  color: #cc7832;
+  font-family: monospace;
+}
+
+ul.trace {
+  font-size: 13px;
+  list-style-type: none;
+  padding-left: 0px;
+}
+
+ul.trace li {
+  color: white;
+  margin-left: 14px;
+  text-indent: -14px;
+}
+
+ul.trace li .function {
+  /* From HLJS's .hljs-section, .hljs-title, .hljs-type */
+  color: #ffc66d;
+  font-family: monospace;
+  font-weight: 600;
+}
+
 .elevation-z4 {
   box-shadow: 0px 2px 4px -1px rgba(0, 0, 0, 0.2),
       0px 4px 5px 0px rgba(0, 0, 0, 0.14),