fix(a11y): unset custom color of storybook left chevrons (#2595)

Author: Mnickii

.storybook/manager-head.html

@@ -292,6 +292,13 @@
     color: #616159 !important;
   }
 
+  /* Fix color contrast of left expanded/collapsed chevrons */
+
+  .sto-bt79wf,
+  .sto-1j9r8vi {
+    color: unset;
+  }
+
   /* Removes Find component feature */
   .css-8ktt77 {
     display: none;