Remove `optgroup` element

In modern-normalize.css file, there is a reset for form elements:

/**
1. Change the font styles in all browsers.
2. Remove the margin in Firefox and Safari.
*/

button,
input,
optgroup,
select,
textarea {
	font-family: inherit; /* 1 */
	font-size: 100%; /* 1 */
	line-height: 1.15; /* 1 */
	margin: 0; /* 2 */
}

button, input, selectandtextareaseem fine butoptgroupis unnecessary; why you may ask, becauseoptgroupshould be a child element ofselectandoptgroupshould be a parent element ofoptionelement, we can remove it to take advantage of cascading whichselect` element does when it inherits.