Border Corner Shape Scoop Doesn't Work

Border corner shape scoop doesn't work

Using Radial Gradients:

Here is another alternative method to achieve the border corner scoop effect using radial gradients. In this method, we use multiple radial gradients and position them at the corners.

.border-scoop {

  height: 300px;

  width: 300px;

  background: -webkit-radial-gradient(0% 100%, circle, transparent 15%, steelblue 15%) no-repeat, -webkit-radial-gradient(100% 0%, circle, transparent 15%, steelblue 15%) no-repeat, -webkit-radial-gradient(0% 0%, circle, transparent 15%, steelblue 15%) no-repeat, -webkit-radial-gradient(100% 100%, circle, transparent 15%, steelblue 15%) no-repeat;

  background: radial-gradient(circle at 0% 100%, transparent 15%, steelblue 15%) no-repeat, radial-gradient(circle at 100% 0%, transparent 15%, steelblue 15%) no-repeat, radial-gradient(circle at 0% 0%, transparent 15%, steelblue 15%) no-repeat, radial-gradient(circle at 100% 100%, transparent 15%, steelblue 15%) no-repeat;

  background-position: 0% 100%, 100% 0%, 0% 0%, 100% 100%;

  background-size: 75% 75%;

}

body {

  background: -webkit-linear-gradient(90deg, crimson, indianred, purple);

  background: linear-gradient(90deg, crimson, indianred, purple);

}

<div class="border-scoop"></div>

CSS- how to give an object with scooped corners a border colour?

I did it with pure css in this example using 4 extra divs:

If youre worried about overflow you can just wrap it in an extra div.

JS FIDDLE

css:

.corner {
background:#fff;
height:20px;
width:20px;    
position:absolute;
}
#sw {
left: -2px;
bottom: -2px;
border-radius: 0px 20px 0px 0px;
border-top: 2px solid #000;
border-right: 2px solid #000;
}
#se {
right: -2px;
bottom: -2px;
border-radius: 20px 0px 0px 0px;
border-top: 2px solid #000;
border-left: 2px solid #000;
}
#nw {
left: -2px;
top: -2px;
border-radius: 0px 0px 20px 0px;
border-bottom: 2px solid #000;
border-right: 2px solid #000;
}
#ne {
right: -2px;
top: -2px;
border-radius: 0px 0px 0px 20px;
border-bottom: 2px solid #000;
border-left: 2px solid #000;
}

.box {
    position:relative;
    height:200px;
    width:200px;
    border: solid 2px black;
    background:blue;
    border-radius: 5px -5px 5px 5px;
}

html:

<div class="box">
    <div id="ne"  class="corner"></div>
    <div id="nw" class="corner"></div>
    <div id="se" class="corner"></div>
    <div id="sw" class="corner"></div>
</div>

Inset border-radius with CSS3

The best way I've found to achieve this with all CSS and HTML (no images, etc.) is by using CSS3 gradients, per Lea Verou. From her solution:

div.round {
    background:
        -moz-radial-gradient(0 100%, circle, rgba(204,0,0,0) 14px, #c00 15px),
        -moz-radial-gradient(100% 100%, circle, rgba(204,0,0,0) 14px, #c00 15px),
        -moz-radial-gradient(100% 0, circle, rgba(204,0,0,0) 14px, #c00 15px),
        -moz-radial-gradient(0 0, circle, rgba(204,0,0,0) 14px, #c00 15px);
    background:
            -o-radial-gradient(0 100%, circle, rgba(204,0,0,0) 14px, #c00 15px),
            -o-radial-gradient(100% 100%, circle, rgba(204,0,0,0) 14px, #c00 15px),
            -o-radial-gradient(100% 0, circle, rgba(204,0,0,0) 14px, #c00 15px),
            -o-radial-gradient(0 0, circle, rgba(204,0,0,0) 14px, #c00 15px);
    background:
            -webkit-radial-gradient(0 100%, circle, rgba(204,0,0,0) 14px, #c00 15px),
            -webkit-radial-gradient(100% 100%, circle, rgba(204,0,0,0) 14px, #c00 15px),
            -webkit-radial-gradient(100% 0, circle, rgba(204,0,0,0) 14px, #c00 15px),
            -webkit-radial-gradient(0 0, circle, rgba(204,0,0,0) 14px, #c00 15px);
    background-position: bottom left, bottom right, top right, top left;
        -moz-background-size: 50% 50%;
        -webkit-background-size: 50% 50%;
    background-size: 50% 50%;
    background-repeat: no-repeat;
}

The net result is a set of transparent gradients with curves. See the full JSFiddle for a demo and to play around with the way it looks.

Obviously this depends on support for rgba and gradient, and accordingly should be treated as a progressive enhancement, or if it's essential to the design, you should supply an image-based fallback for older browsers (especially IE, which doesn't support gradient even up through IE9).

CSS 3 Shape: Inverse Circle or Cut Out Circle

Update: CSS3 Radial Background Gradient Option

(For those browsers supporting it--tested in FF and Chrome--IE10, Safari should work too).

One "problem" with my original answer is those situations where one does not have a solid background that they are working against. This update creates the same effect allowing for a transparent "gap" between the circle and it's inverse cutout.

See example fiddle.

CSS

.inversePair {
    border: 1px solid black;
    display: inline-block;    
    position: relative;    
    height: 100px;
    text-align: center;
    line-height: 100px;
    vertical-align: middle;
}

#a {
    width: 100px;
    border-radius: 50px;
    background: grey;
    z-index: 1;
}

#b {
    width: 200px;
    /* need to play with margin/padding adjustment
       based on your desired "gap" */
    padding-left: 30px;
    margin-left: -30px;
    /* real borders */
    border-left: none;
    -webkit-border-top-right-radius: 20px;
    -webkit-border-bottom-right-radius: 20px;
    -moz-border-radius-topright: 20px;
    -moz-border-radius-bottomright: 20px;
    border-top-right-radius: 20px;
    border-bottom-right-radius: 20px;
    /* the inverse circle "cut" */
    background-image: -moz-radial-gradient(
        -23px 50%, /* the -23px left position varies by your "gap" */
        circle closest-corner, /* keep radius to half height */
        transparent 0, /* transparent at center */
        transparent 55px, /*transparent at edge of gap */
        black 56px, /* start circle "border" */
        grey 57px /* end circle border and begin color of rest of background */
    );
    background-image: -webkit-radial-gradient(-23px 50%, circle closest-corner, rgba(0, 0, 0, 0) 0, rgba(0, 0, 0, 0) 55px, black 56px, grey 57px);
    background-image: -ms-radial-gradient(-23px 50%, circle closest-corner, rgba(0, 0, 0, 0) 0, rgba(0, 0, 0, 0) 55px, black 56px, grey 57px);
    background-image: -o-radial-gradient(-23px 50%, circle closest-corner, rgba(0, 0, 0, 0) 0, rgba(0, 0, 0, 0) 55px, black 56px, grey 57px);
    background-image: radial-gradient(-23px 50%, circle closest-corner, rgba(0, 0, 0, 0) 0, rgba(0, 0, 0, 0) 55px, black 56px, grey 57px);
}

Original Answer

Took more effort than I expected to get the z-indexing to work (this seems to ignore the negative z-index), however, this gives a nice clean look (tested in IE9, FF, Chrome):

HTML

<div id="a" class="inversePair">A</div>
<div id="b" class="inversePair">B</div>

CSS

.inversePair {
    border: 1px solid black;
    background: grey;
    display: inline-block;    
    position: relative;    
    height: 100px;
    text-align: center;
    line-height: 100px;
    vertical-align: middle;
}

#a {
    width: 100px;
    border-radius: 50px;
}

#a:before {
    content:' ';
    left: -6px;
    top: -6px;
    position: absolute;
    z-index: -1;
    width: 112px; /* 5px gap */
    height: 112px;
    border-radius: 56px;
    background-color: white;
} 

#b {
    width: 200px;
    z-index: -2;
    padding-left: 50px;
    margin-left: -55px;
    overflow: hidden;
    -webkit-border-top-right-radius: 20px;
    -webkit-border-bottom-right-radius: 20px;
    -moz-border-radius-topright: 20px;
    -moz-border-radius-bottomright: 20px;
    border-top-right-radius: 20px;
    border-bottom-right-radius: 20px;
}

#b:before {
    content:' ';
    left: -58px;
    top: -7px;
    position: absolute;
    width: 114px; /* 5px gap, 1px border */
    height: 114px;
    border-radius: 57px;
    background-color: black;
}

How to add shadow to reverse c radial gradient only at the edges?

Since you are already using a radial-gradient to create the border corner scoop shape, all that is needed is to add an extra color-stop position in between to produce the shadow effect.

In the below snippet, we use the following gradient (for each corner):

radial-gradient(circle at 0 100%, rgba(204, 0, 0, 0) 100px, #AAA 104px, #f7f6f6 105px)

This gradient can be interpreted as follows:

The color of the radial gradient is rgba(204, 0, 0, 0) upto 100px radius from the center of the circle. The color is a transparent color and produces the effect of a reverse C cut (or a scoop).
From the 100px radius to 104px radius, the color gradually changes from rgba(204, 0, 0, 0) to #AAA (greyish color) and this produces a shadow like effect. You can change the color of the shadow by changing this color value.
Between 104px and 105px radius, color of the gradient changes from #AAA to #f7f6f6 which makes it look the color is changing smoothly instead of a hard-stop.

div {

  background: -moz-radial-gradient(0 100%, circle, rgba(204, 0, 0, 0) 100px, #AAA 104px, #f7f6f6 105px), -moz-radial-gradient(100% 100%, circle, rgba(204, 0, 0, 0) 100px, #AAA 104px, #f7f6f6 105px), -moz-radial-gradient(100% 0, circle, rgba(204, 0, 0, 0) 100px, #AAA 104px, #f7f6f6 105px), -moz-radial-gradient(0 0, circle, rgba(204, 0, 0, 0) 100px, #AAA 104px, #f7f6f6 105px);

  background: -webkit-radial-gradient(0 100%, circle, rgba(204, 0, 0, 0) 100px, #AAA 104px, #f7f6f6 105px), -webkit-radial-gradient(100% 100%, circle, rgba(204, 0, 0, 0) 100px, #AAA 104px, #f7f6f6 105px), -webkit-radial-gradient(100% 0, circle, rgba(204, 0, 0, 0) 100px, #AAA 104px, #f7f6f6 105px), -webkit-radial-gradient(0 0, circle, rgba(204, 0, 0, 0) 100px, #AAA 104px, #f7f6f6 105px);

  background: radial-gradient(circle at 0 100%, rgba(204, 0, 0, 0) 100px, #AAA 104px, #f7f6f6 105px), radial-gradient(circle at 100% 100%, rgba(204, 0, 0, 0) 100px, #AAA 104px, #f7f6f6 105px), radial-gradient(circle at 100% 0, rgba(204, 0, 0, 0) 100px, #AAA 104px, #f7f6f6 105px), radial-gradient(circle at 0 0, rgba(204, 0, 0, 0) 100px, #AAA 104px, #f7f6f6 105px);

  background-position: bottom left, bottom right, top right, top left;

  background-size: 50% 50%;

  background-repeat: no-repeat;

  height: 300px;

  width: 500px;

}

<div></div>

Rounded table corners CSS only

Seems to work fine in FF and Chrome (haven't tested any others) with separate borders: http://jsfiddle.net/7veZQ/3/

Edit: Here's a relatively clean implementation of your sketch:

table {
    border-collapse:separate;
    border:solid black 1px;
    border-radius:6px;
}

td, th {
    border-left:solid black 1px;
    border-top:solid black 1px;
}

th {
    background-color: blue;
    border-top: none;
}

td:first-child, th:first-child {
     border-left: none;
}

<table>
    <thead>
    <tr>
        <th>blah</th>
        <th>fwee</th>
        <th>spoon</th>
    </tr>
    </thead>
    <tr>
        <td>blah</td>
        <td>fwee</td>
        <td>spoon</td>
    </tr>
    <tr>
        <td>blah</td>
        <td>fwee</td>
        <td>spoon</td>
    </tr>
</table>

Border Corner Shape Scoop Doesn't Work