Editing Module:Chem2/styles.css

.template-chem2-su { /* {{pp-template}} */
	display: inline-block;
	font-size: 80%;
	line-height: 1;
	vertical-align: -0.35em;
}

.template-chem2-su > span {
	display: block;
}

/* Ignore the linter error about this selector being "overqualified"; this is the
   correct selector to override the default stylesheet. */
sub.template-chem2-sub {
	font-size: 80%;
	vertical-align: -0.35em;
}

sup.template-chem2-sup {
	font-size: 80%;
	vertical-align: 0.65em;
}