Update style.css

removed errors shown in W3C CSS Validator:


12		Value Error : font-weight bolder is not a font-weight value : bolder
412	input.button	Value Error : position top is not a position value : top
659	.youtube-player	Value Error : margin-left Too many values or values are not recognized : 10px auto
660	.youtube-player	Value Error : margin-bottom Too many values or values are not recognized : 10px auto

Note: Last two were already commented out by (Paul ?)