How to implement curve background in CSS?

Question

I have a landing page with a curve background. Please refer to the following image. I would like to know the best approach when coding this from CSS. I also need to make this responsive and I'm using bootstrap as a CSS framework. Following is what I have done.

I have used an SVG image as the background and used it with :before pseudo-class to display in the bottom. And also I have removed width and height from the SVG and kept the view box and added preserveAspectRatio="xMinYMin meet" to SVG to make it responsive. (Please note these attributes not added to the example in JSFiddle)

What is the best approach to create these curvy backgrounds?

JSFIDDLE

.hero-container {
  background-image: url(https://images.unsplash.com/photo-1581362508717-f542c1ecf295?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=1651&q=80);
  background-size: cover;
  background-repeat: no-repeat;
  background-position: top center;
  padding: 16.625rem 0;
}

.hero-container:after {
  content: url('http://svgshare.com/i/Hud.svg');
  position: absolute;
  width: 100%;
  height: auto;
  bottom: -85px;
}

<link rel="stylesheet" type="text/css" href="https://stackpath.bootstrapcdn.com/bootstrap/4.4.1/css/bootstrap.css">
<section class="hero-container position-relative">
  <div class="container">
    <div class="row">
      <div class="col-md-7 col-xs-12">
        <h1 class="mb-3">Lorem ipsum dolor sit amet</h1>
        <p class="mb-4 text-white">Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet</p>
        <button class="btn btn-secondary">Register My Club</button>
      </div>
    </div>
  </div>
</section>

Answer 1

I will consider the same idea as this previous answer to create the curve using mask and radial-gradient. Simply adjust both variables until you get the needed result:

.box {
  height:300px;
  background: url(https://images.unsplash.com/photo-1581362508717-f542c1ecf295?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=1651&q=80) center/cover;
  -webkit-mask:
    radial-gradient(var(--r1,100%) var(--r2,50%) at top   ,white 79.5%,transparent 80%) top left,
    radial-gradient(var(--r1,100%) var(--r2,50%) at bottom,transparent 79.5%,white 80%) top center,
    radial-gradient(var(--r1,100%) var(--r2,50%) at top   ,white 79.5%,transparent 80%) top right;
  mask:
    radial-gradient(var(--r1,100%) var(--r2,50%) at top   ,white 79.5%,transparent 80%) top left,
    radial-gradient(var(--r1,100%) var(--r2,50%) at bottom,transparent 79.5%,white 80%) top center,
    radial-gradient(var(--r1,100%) var(--r2,50%) at top   ,white 79.5%,transparent 80%) top right;
   /* adjust the 150% to control the covered area, the bigger the value the bigger the area will be*/
  -webkit-mask-size:33.4% 150%;
  -webkit-mask-repeat:no-repeat;
  mask-size:33.4% 150%;
  mask-repeat:no-repeat;
}

<div class="box" style="--r1:130%;--r2:71.5%">

</div>

To understand the trick replace the mask with background:

.box {
  height:300px;
  background:
    radial-gradient(var(--r1,100%) var(--r2,50%) at top   ,red 79.5%,transparent 80%)  top left,
    radial-gradient(var(--r1,100%) var(--r2,50%) at bottom,transparent 79.5%,blue 80%) top center,
    radial-gradient(var(--r1,100%) var(--r2,50%) at top   ,red 79.5%,transparent 80%)  top right;
  mask:
    radial-gradient(var(--r1,100%) var(--r2,50%) at top   ,red 79.5%,transparent 80%)  top left,
    radial-gradient(var(--r1,100%) var(--r2,50%) at bottom,transparent 79.5%,blue 80%) top center,
    radial-gradient(var(--r1,100%) var(--r2,50%) at top   ,red 79.5%,transparent 80%)  top right;
  background-size:33.4% 150%;
  background-repeat:no-repeat;
  border:1px solid;
}

<div class="box" style="--r1:130%;--r2:71.5%">

</div>

---

Applying this to your code:

.hero-container {
  background: url(https://images.unsplash.com/photo-1581362508717-f542c1ecf295?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=1651&q=80) top/cover;
  padding: 16.625rem 0;
  -webkit-mask:
    radial-gradient(var(--r1,160%) var(--r2,68.15%) at top   ,white 79.5%,transparent 80%) top left,
    radial-gradient(var(--r1,160%) var(--r2,68.15%) at bottom,transparent 79.5%,white 80%) top center,
    radial-gradient(var(--r1,160%) var(--r2,68.15%) at top   ,white 79.5%,transparent 80%) top right;
  mask:
    radial-gradient(var(--r1,160%) var(--r2,68.15%) at top   ,white 79.5%,transparent 80%) top left,
    radial-gradient(var(--r1,160%) var(--r2,68.15%) at bottom,transparent 79.5%,white 80%) top center,
    radial-gradient(var(--r1,160%) var(--r2,68.15%) at top   ,white 79.5%,transparent 80%) top right;
  -webkit-mask-size:33.4% 140%; 
  -webkit-mask-repeat:no-repeat;
  mask-size:33.4% 140%;
  mask-repeat:no-repeat;
}

<link rel="stylesheet" type="text/css" href="https://stackpath.bootstrapcdn.com/bootstrap/4.4.1/css/bootstrap.css">
<section class="hero-container position-relative">
  <div class="container">
    <div class="row">
      <div class="col-md-7 col-xs-12">
        <h1 class="mb-3">Lorem ipsum dolor sit amet</h1>
        <p class="mb-4 text-white">Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet</p>
        <button class="btn btn-secondary">Register My Club</button>
      </div>
    </div>
  </div>
</section>