How can I make a curve border using CSS3? [duplicate] - css

Question

This question already has answers here:
Curve bottom side of the div to the inside with CSS
(2 answers)
Closed 4 years ago.
I have added 2 pictures here. You can see that first curve is down curve and second one is up curve.
Now, I have a rectangle box using CSS. I want to make the top and bottom border should be like the picture.
I can use CSS border-radius property to make a border curve. But I don't understand how can I make this type of border curve using CSS3?
Updated:
Here is the full output I desire:

Answer 1

I used before after to achieve this
div{
width: 400px;
height: 200px;
background-color: #333;
position: relative;
overflow: hidden;
}
div:before {
content: "";
position: absolute;
top: -10%;
width: 100%;
height: 50%;
background-color: white;
border-bottom-left-radius: 50%;
border-bottom-right-radius: 50%;
}
div:after {
content: "";
position: absolute;
width: 100%;
bottom: -10%;
height: 50%;
background-color: white;
border-top-left-radius: 50%;
border-top-right-radius: 50%;
}
<div></div>
Update
after OP's recent comment, here you can add content in content-main div
.content{
background-color: #333;
width: 400px;
}
.content-top, .content-bottom{
width: 400px;
height: 100px;
background-color: #333;
position: relative;
overflow: hidden;
}
.content-top:before {
content: "";
position: absolute;
top: -10%;
width: 100%;
height: 50%;
background-color: white;
border-bottom-left-radius: 50%;
border-bottom-right-radius: 50%;
}
.content-bottom:after {
content: "";
position: absolute;
width: 100%;
bottom: -10%;
height: 50%;
background-color: white;
border-top-left-radius: 50%;
border-top-right-radius: 50%;
}
.content-main{
padding: 10px;
}
<div class="content">
<div class="content-top"></div>
<div class="content-main">
<h1>Cat</h1>
<img src="https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcS11TbGOYA0EmL-usNpArFE8o17OSRSilYYohX1lgyxaP43M2Pt">
</div>
<div class="content-bottom"></div>
</div>

Answer 2

You can achieve this using two Divs one with black background and the children with white background and rounded borders. The wrapper should have a padding to simulate border thickness:
#wrapper{
background:#000000;
width:600px;
height:200px;
padding:10px;
}
#roundCurve{
background:#ffffff;
width:600px;
height:200px;
border-bottom-left-radius:50% 50px;
border-bottom-right-radius:50% 50px;
border-top-left-radius:50% 50px;
border-top-right-radius:50% 50px;
}
<div id="wrapper">
<div id="roundCurve"></div>
</div>

Answer 3

Here is an example you can follow:
body {
background: black;
}
.roundCorner {
width: 150px;
height: 100px;
padding: 2em;
border-bottom: 0;
position: relative;
background: white;
border-radius: 1em 1em 0 0;
}
.roundCorner:before {
position: absolute;
left: -1px;
right: -1px;
top: 0;
height: 1.5em;
border: 1px solid black;
border-top: 0;
border-radius: 0 0 3em 3em;
content:'';
background: black;
}
.roundCorner:after {
position: absolute;
left: -1px;
right: -1px;
bottom: 0;
height: 1.5em;
border: 1px solid black;
border-bottom: 0;
border-radius: 3em 3em 0 0;
content: '';
background: black;
}
<div class="roundCorner"></div>
You can change background of body, .roundCorner, .roundCorner:before, .roundCorner:after to see how it's working.