There are numerous methods available to create the desired shape. Here is an extensive breakdown of the options:

Approaches Using SVG:

Scalable Vector Graphics (SVG) is highly recommended for creating complex shapes due to its simplicity and scalability. Below are a couple of techniques that can be employed:

1- Utilizing Path Element:

The path element within SVG can be utilized to craft the required shape with solid colors, gradients, or patterns.

Only the attribute d is essential for defining shapes using the path element. This attribute consists of concise commands and parameters necessary for shaping.

Here is the code snippet needed to generate this shape:

<path d="M 0,0
         L 0,40
         Q 250,80 500,40
         L 500,0
         Z" />

Below is a brief explanation of the path commands used in the above code:

• M command specifies the starting point for drawing.
• L command draws straight lines.
• Q command creates curves.
• Z command closes the current path.

Output Image:

https://i.sstatic.net/SIVaB.png

Live Demo:

svg {
  width: 100%;
}

<svg width="500" height="80" viewBox="0 0 500 80" preserveAspectRatio="none">
  <path d="M0,0 L0,40 Q250,80 500,40 L500,0 Z" fill="black" />
</svg>

2- Clipping Method:

Clipping involves concealing or eliminating certain components of an element.

In this method, a clipping region is defined using the clipPath element in SVG and then applied to a rectangular element. Sections outside this designated area will be hidden from view.

Here is the pertinent code segment:

<defs>
    <clipPath id="shape">
        <path d="M0,0 L0,40 Q250,80 500,40 L500,0 Z" />
    </clipPath>
</defs>
<rect x="0" y="0" width="500" height="80" fill="#000" clip-path="url(#shape)" />

A quick explanation of the elements utilized in the above code:

• defs defines objects for later use within the SVG document.
• clipPath establishes a clipping region.
• rect generates rectangles.
• clip-path links to the previously created clipping path.

Live Demo:

svg {
  width: 100%;
}

<svg width="500" height="80" viewBox="0 0 500 80" preserveAspectRatio="none">
  <defs>
    <clipPath id="shape">
      <path d="M0,0 L0,40 Q250,80 500,40 L500,0 Z" />
    </clipPath>
  </defs>
  <rect x="0" y="0" width="500" height="80" fill="#000" clip-path="url(#shape)" />
</svg>

CSS Techniques:

1- Leveraging Pseudo Elements:

One can make use of ::before or ::after pseudo-elements to achieve this shape. The steps for implementation are outlined below:

• Create a layer using either ::before or ::after with dimensions larger than its parent element.
• Apply border-radius to introduce rounded edges.
• Add overflow: hidden on the parent container to mask unnecessary parts.

Required HTML structure:

A single div element, possibly with a class like shape, suffices:

<div class="shape"></div>

Live Demo:

.shape {
  position: relative;
  overflow: hidden;
  height: 80px;
}

.shape::before {
  border-radius: 100%;
  position: absolute;
  background: black;
  right: -200px;
  left: -200px;
  top: -200px;
  content: '';
  bottom: 0;
}

<div class="shape"></div>

2- Radial Gradient Approach:

This technique employs CSS3's radial-gradient() function to render the shape as a background on an element. While effective, it might result in slightly pixelated corners.

Required HTML markup:

Simply a solitary div element with a relevant class declaration:

<div class="shape"></div>

Necessary CSS styles:

.shape {
  background-image: radial-gradient(120% 120px at 50% -30px, #000 75%, transparent 75%);
}

Live Demo:

.shape {
  background: radial-gradient(120% 120px at 50% -30px, #000 75%, transparent 75%) no-repeat;
  height: 80px;
}

<div class="shape"></div>

Javascript Approaches:

Although not mandatory for this scenario, I'll include a JavaScript approach for comprehensive understanding. This can be beneficial in specific scenarios as well:

HTML5 Canvas Implementation:

We can draw the specified shape on an HTML5 Canvas using various path functions:

var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');

ctx.beginPath();
ctx.moveTo(0, 0);
ctx.lineTo(0, 40);
ctx.quadraticCurveTo(311, 80, 622, 40);
ctx.lineTo(622, 0);
ctx.fill();

<canvas id="canvas" width="622" height="80"></canvas>

Here's a brief overview of the methods utilized in the aforementioned code:

• beginPath() initiates a new path for subsequent drawing operations.
• moveTo(x, y) relocates the pen to specified coordinates.
• lineTo(x, y) draws straight lines from the current pen position.

• quadraticCurveTo(cp1x, cp1y, x, y)

  facilitates curve creation using control points.
• fill() fills the current path according to the winding rule.

Additional Resources:

• For Radial Gradient: Specifications, MDN Reference
• Regarding SVG: Official Documentation, Mozilla Developer Network
• References on HTML5 Canvas: Canvas Specifications, Useful MDN Link

Here is the solution you've been looking for:

div {
  background-color: black;
  width: 250px;
  height: 100px;
  border-radius: 0 0 50% 50% / 50px;
}

<div></div>

This code snippet works flawlessly even when adjusting the height of the div.

You have the ability to achieve this effect using CSS. Simply adjust the width of your div to extend beyond the page in order to create a less rounded appearance on the edges. You can then reposition the div to the left to compensate for the extended width, and apply a bottom border radius with values for both the x and y axes. Utilize a negative bottom margin to fill any gap that may appear:

.round-bottom { 
  border-bottom-left-radius: 50% 200px; // semi-circle spanning half & up by 200px at the left side
  border-bottom-right-radius: 50% 200px; // semi-circle spanning half & up by 200px at the right side
  width: 160%; overflow: hidden; // increase size and hide overflowing parts
  margin-bottom: -50px; // add negative margin to fill bottom gap
  position: relative; left:-30%; // readjust element positioning to account for extra width on each side (may require display:block;)
}

.round-bottom { 
  border-bottom-left-radius: 50% 150px !important;
  border-bottom-right-radius: 50% 150px !important;
  position: relative;
  overflow: hidden;
  width: 160%; 
  margin-bottom:-50px;
  left:-30%; 
  background-color:#444;
  background-image: url('https://upload.wikimedia.org/wikipedia/commons/a/a2/Tropical_Forest_with_Monkeys_A10893.jpg'); background-position: center center;
  background-size: 42% auto;
  height:150px;
}
.container { width: 100%; height: height:100px; padding-bottom:50px; overflow:hidden;}

<div class="container"><div class="round-bottom"></div></div>

Give this a try

.navigation-bar{
    border-radius:50% 50% 0 0;
    -webkit-border-radius:50% 50% 0 0;
    background:#000;
    min-height:100px;
}

Check out the updated jsFiddle File here

If someone is looking for a similar but reverse version of this code (for my situation)

<svg
 height="80"
 viewBox="0 0 500 80"
 preserveAspectRatio="none"
 className="w-full"
>
<path d="M0,0 Q250,80 500,0 L500,80 L0,80 Z" fill="black" fill- 
 rule="evenodd" />
</svg>

Feel free to adjust the height as needed.