Box with inside curve - html

Question

I've been trying to create a an 'inside curved box' with no success, I don't seem to find any example online. Can anyone help me to replicate that using just CSS or maybe SVG?

Answer 1

Given that the shape background is a solid color and the page background is not, you can create the shape using a pseudo-element and a box-shadow with high spread radius. Its a hackish solution but would work on most browsers as box shadow has good support.
div{
position: relative;
height: 300px;
width: 150px;
border-radius: 12px;
overflow: hidden;
}
div:after{
position: absolute;
content: '';
height: 30px;
bottom: -15px;
width: 100%;
left: 0px;
box-shadow: 0px 0px 0px 500px blue;
border-radius: 12px;
}
body{
background: linear-gradient(chocolate, brown);
height: 100vh;
}
<div class='shape'></div>
You can also achieve the same effect using SVG path elements like in the below snippet.
div {
height: 300px;
width: 150px;
}
svg path {
fill: blue;
}
body {
background: linear-gradient(chocolate, brown);
height: 100vh;
}
<svg viewBox='0 0 150 300' height='0' width='0'>
<defs>
<g id='shape'>
<path d='M0,12 A12,12 0 0,1 12,0 L138,0 A12,12 0 0,1 150,12 L150,300 A12,12 0 0,0 138,288 L12,288 A12,12 0 0,0 0,300z' id='fill' />
</g>
</defs>
</svg>
<div class='shape'>
<svg viewBox='0 0 150 300' preserveAspectRatio='none' vector-effect='non-scaling-stroke'>
<use xlink:href='#shape' />
</svg>
</div>