The "Use Legacy Vector" is not indented properly, all the other options have a padding-left of 7%. The "Use Legacy Vector" options has the class mw-htmlform-field-Vector\HTMLForm\Fields\HTMLLegacySkinVersionField, which does not match the rule that adds the padding, which matches something like mw-htmlform-field-HTMLCheckField. Since the rule seems to match every class that starts with .mw-htmlform-field- and is really long, a rule like [class^="mw-htmlform-field-"] might be better to use.
Here how it currently looks:
