CSS Class by element ID?

I have a following css

#container
{
        border:1px solid black;
}
#container #header
{
    color:blue;
}

#container #footer
{
    color:red;
}

Can i write it as

#container
{
        border:1px solid black;
        #header
        {
            color:blue开发者_开发问答;
        }

        #footer
        {
            color:red;
        }
}

So the #header and #footer are still select as #container's childs element. Or i need to use some css framework like .LESS ?

Nope, CSS doesn't support that. I agree, it would be useful. However, you're right, it looks like LESS supports it.

Yes only if you use SASS, not possible in vanilla CSS.

CSS doesn't support that syntax out of the box, so yes you would have to use .LESS