Border radius to curve inwards?

How can I have the border to curve inwards instead of outwards?

For instance - this is curving outwards:

header {
  position: relative;
  height: 300px;
  background-image: linear-gradient(#ff9d2f, #ff6126);
  border-bottom-left-radius: 50% 20%;
  border-bottom-right-radius: 50% 20%;
}

h1 {
  margin: 0;
  padding: 100px 0;
  font: 44px "Arial";
  text-align: center;
}

header h1 {
  color: white;
}

<header>
  <h1>Header Content</h1>
</header>

<section>
  <h1>Section Content</h1>
</section>

I would like it to curve inwards, is it possible?

Border radius to curve inwards?

2 Answers