how to get transparent for the div?

Question

Does CSS gives any option to show background image at the corner a transparent.

instead of showing white background in (DEMO)

avoid white area

#octagon {
    width: 100px;
    height: 100px;
    background: red;
    position: relative;
    margin: 50px auto 0;
}

#octagon:before {
    content: "";
    position: absolute;
    top: 0;
    left: 0;
    border-bottom: 29px solid red;
    border-left: 29px solid red;
    border-right: 29px solid #eee;
    width: 42px;
    height: 0;
}

http://jsfiddle.net/L8JUJ/4/

Answer 1

Working Fiddle

Made small changes and adjustments in margins.

CSS:

body{
    background: url(http://placehold.it/350x150&text=FooBar1) repeat;
}
#octagon {
    width: 100px;
    height: 71px;
    background: red;
    position: relative;
    margin: 99px 10px 0px 100px;
}

#octagon:before {
    content: "";
    position: absolute;
    top: -29px;
    left: 0;
    border-bottom: 29px solid red;
    border-left: 29px solid red;
    border-right: 29px solid transparent;
    width: 42px;
    height: 0;
}

Answer 2

#octagon:before {
content: "";
position: absolute;
top: 0;
left: 0;
border-bottom: 29px solid red;
border-left: 29px solid red;
border-right: 29px solid #eee;
width: 42px;
height: 0;
opacity:0.6;

}

Answer 3

For a transparent border you can modify #octagon:before border-right with

border-right: 29px solid rgba(0,0,0,0.5);

That will not give you the effect you want because in the back there is the element that already has a background color, so the only way to do this and work would be to add some js to your code, such as: http://jquery.malsup.com/corner/