replace gray colors

src/client/styles/scss/_override-bootstrap-variables.scss

@@ -27,6 +27,10 @@ $red: #ff0a54 !default;
 
 //== Typography
 //
+$gray-400: $gray-300;
+$gray-500: $gray-400;
+$gray-600: $gray-500;
+
 //## Font, line-height, and color for body text, headings, and more.
 $font-family-sans-serif:  Lato, -apple-system, BlinkMacSystemFont, 'Hiragino Kaku Gothic ProN', Meiryo, sans-serif;
 $font-family-serif:       Georgia, "Times New Roman", Times, serif;