gh-142363: Improve Tachyon flamegraph contrast (#142377)

Author: hugovk

Lib/profiling/sampling/_flamegraph_assets/flamegraph.css

@@ -789,7 +789,7 @@ body.resizing-sidebar {
 .tooltip-location {
   font-family: var(--font-mono);
   font-size: 11px;
-  color: var(--text-muted);
+  color: var(--text-secondary);
   background: var(--bg-tertiary);
   padding: 4px 8px;
   border-radius: 4px;

Lib/profiling/sampling/_shared_assets/base.css

@@ -44,7 +44,7 @@
 
   --text-primary: #2e3338;
   --text-secondary: #5a6c7d;
-  --text-muted: #8b949e;
+  --text-muted: #6f767e;
 
   --accent: #3776ab;
   --accent-hover: #2d5aa0;
@@ -91,7 +91,7 @@
 
   --text-primary: #e6edf3;
   --text-secondary: #8b949e;
-  --text-muted: #6e7681;
+  --text-muted: #757e8a;
 
   --accent: #58a6ff;
   --accent-hover: #79b8ff;