CSS Make a div curved at top and bottom but straight at the left and right sides

Question

Hey guys I've been wondering if it was possible to do this, I've tried with border-radius but it only makes curves to the left and right sides apparently...

Here's what I need:

This would be the working div:

#mainbox {
  width: 115px;
  height: 24px;
  background-color: gray;
  border: 1px solid #000000;
  text-align: center;
}

<div id="mainbox">
  <div id="secondbox">test</div>
</div>

Any possible ideas?

Answer 1

Something like this can be achieved but it's troublesome. SVG will be better for this.

Referenced from this question on SO.

body {
  width: 100%;
  height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
}

#mainbox {
  width: 200px;
  height: 130px;
  overflow: hidden;
  position: relative;
  display: flex;
  align-items: flex-end;
  justify-content: center;
}

#mainbox::before,
#mainbox::after {
  content: "";
  display: block;
  position: absolute;
  height: 100px;
  /* equal to inner curvedbox */
  border-left: 5px solid black;
  bottom: 0;
  z-index: 1;
}

#mainbox::before {
  left: 0;
}

#mainbox::after {
  right: 0;
}

#curvedbox {
  position: relative;
  width: 100%;
  height: 100px;
  display: flex;
  align-items: center;
  justify-content: center;
}

#curvedbox::before,
#curvedbox::after {
  display: block;
  content: "";
  width: 140%;
  height: 200%;
  border: solid 5px #000;
  border-color: #000 transparent transparent transparent;
  border-radius: 100%;
  position: absolute;
  left: 50%;
  transform: translateX(-50%);
}

#curvedbox::before {
  top: -30%;
}

#curvedbox::after {
  top: 69%;
}

#secondbox {
  transform: translateY(-140%);
}

<div id="mainbox">
  <div id="curvedbox">
    <div id="secondbox">test</div>
  </div>
</div>