fix: Remove unnecessary background color from wizard header (#3343)

Author: cansuaa

src/wizard/styles.scss

@@ -226,7 +226,6 @@
   display: contents;
 
   > .form-header {
-    background-color: awsui.$color-background-layout-main;
     grid-column: 2;
     grid-row: 1;
     color: awsui.$color-text-body-default;