css - Select child element of element with attribute -

i have button. button has span tag inside of text of button. button may disabled. when disabled, i'd button grey. why doesn't work? first html, css

<button disabled>     <span class="dark-disabled">start new game</span> </button>  button:disabled span{     background: #ccc; } 

but fire if class selector instead:

button:disabled .dark-disabled{     background: #ccc; } 

you looking css attribute selector

button[disabled] span{   background: #ccc; } 

edit:

i misread question, both :disabled , [disabled] work button. sample gave me works fine in firefox: jsfiddle

what browser using?