Improve Tachyon flamegraph contrast

Author: hugovk

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;