Flatten the source code panel

PiperOrigin-RevId: 790779669

Author: Profiler Team

frontend/app/components/graph_viewer/graph_viewer.ng.html

@@ -37,7 +37,7 @@
         [showMetadata]="showMetadata"
       ></hlo-text-view>
     </div>
-    <mat-expansion-panel class="hlo-text-view-panel" *ngIf="sourceCodeServiceIsAvailable">
+    <mat-expansion-panel class="stack-trace-snippet-panel" *ngIf="sourceCodeServiceIsAvailable">
       <mat-expansion-panel-header>
         <mat-panel-title>Stack Trace Source Code Snippets</mat-panel-title>
       </mat-expansion-panel-header>

frontend/app/components/graph_viewer/graph_viewer.scss

@@ -62,6 +62,20 @@ mat-progress-bar {
   z-index: 2;
 }
 
+.stack-trace-snippet-panel {
+  position: sticky;
+  width: 100%;
+  box-shadow: none;
+  border-bottom: .5px solid silver;
+  border-radius: 0;
+}
+
+.stack-trace-snippet-container {
+  min-height: 400px;
+  max-height: 400px;
+  overflow-y: auto;
+}
+
 .graph-container {
   width: 100%;
   height: 100%;
@@ -85,9 +99,3 @@ mat-progress-bar {
 .progress-container-graphviz {
   display: flex;
 }
-
-.stack-trace-snippet-container {
-  min-height: 400px;
-  max-height: 400px;
-  overflow-y: auto;
-}