Add optgroup in Typography

Added 'optgroup' in #Typography via both -
- _typography.scss
&
- style.css
It fixes the odd styling of the select element.

sass/typography/_typography.scss

@@ -2,6 +2,7 @@ body,
 button,
 input,
 select,
+optgroup,
 textarea {
 	color: $color__text-main;
 	font-family: $font__main;

style.css

@@ -264,6 +264,7 @@ body,
 button,
 input,
 select,
+optgroup,
 textarea {
 	color: #404040;
 	font-family: sans-serif;