Neumorphism combines developments of flat design and skeuomorphism. Neumorphism, or soft UI, is a visual style that combines background colors, shapes, gradients, highlights, and shadows to ensure graphic intense buttons and switches. All that allows achieving a soft, extruded plastic look, and almost 3D styling.
For a better understanding visit: https://www.geeksforgeeks.org/html/html-responsive-modal-login-form/
Here is the preview image we are going to make:

Follow the code to create a Neumorphism Signin form using CSS:
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<title>GFG Neumorphism Signin</title>
<meta name="description" content="" />
<meta name="viewport" content="width=device-width,
initial-scale=1" />
<style>
* {
box-sizing: border-box;
}
body {
margin: 0;
/*Display width and height*/
height: 100vh;
width: 100vw;
overflow: hidden;
font-family: "Lato", sans-serif;
font-weight: 700;
/* To make all the elements center */
display: flex;
align-items: center;
justify-content: center;
/*Font color and background Color*/
color: #555;
background: #ecf0f3;
}
.gfg-div {
/* Login Card Width and height */
width: 430px;
height: 500px;
/* padding */
padding: 20px 35px 15px 35px;
border-radius: 35px;
background: #ecf0f3;
/* Box-shadow for 3d visualization*/
box-shadow: -6px -6px 6px rgba(255, 255, 255, 0.8),
6px 6px 6px rgba(0, 0, 0, 0.2);
}
.gfg-logo {
background: url("gfg-logo.png");
background-size: cover;
width: 100px;
height: 100px;
border-radius: 50%;
margin: 0 auto;
/* Box-shadow for logo */
box-shadow: 0px 0px 2px #5f5f5f, 0px 0px 0px 5px #ecf0f3,
8px 8px 15px #a7aaaf, -8px -8px 15px #ffffff;
}
.gfg-title {
text-align: center;
font-size: 28px;
padding-top: 24px;
letter-spacing: 0.5px;
color: #5ed887;
}
.gfg-sub-title {
text-align: center;
font-size: 15px;
padding-top: 7px;
letter-spacing: 3px;
color: #5eaa77;
}
.gfg-input-fields {
width: 100%;
padding: 20px 5px 10px 5px;
}
.gfg-input-fields input {
/* To hide default browser options of input field */
border: none;
outline: none;
/* Custom design for the input field */
background: none;
font-size: 18px;
color: #555;
padding: 15px 10px 15px 5px;
}
.gfg-email,
.gfg-password {
margin-bottom: 20px;
border-radius: 20px;
/* Box-shadow for 3d */
box-shadow: inset 5px 5px 5px #cbced1,
inset -5px -5px 5px #ffffff;
}
.gfg-input-fields svg {
height: 22px;
margin: 0 10px -3px 25px;
}
.gfg-button {
/* To hide default browser options of input field */
outline: none;
border: none;
/* Custom design for the Button */
cursor: pointer;
width: 100%;
height: 60px;
border-radius: 25px;
font-size: 20px;
font-weight: 700;
font-family: "Lato", sans-serif;
color: #fff;
text-align: center;
background: #67d18a;
box-shadow: 7px 7px 8px #cbced1, -7px -7px 8px #ffffff;
transition: 0.5s;
}
.gfg-button:hover {
background: #5fb87d;
}
.gfg-button:active {
background: #4a9764;
}
.gfg-link {
padding-top: 20px;
text-align: center;
}
.gfg-link a {
text-decoration: none;
color: #aaa;
font-size: 15px;
transition: 0.5s;
}
.gfg-link a:hover {
text-decoration: none;
color: #67d18a;
font-size: 15px;
}
</style>
</head>
<body>
<div class="gfg-div">
<div class="gfg-logo"></div>
<div class="gfg-title">Geeksforgeeks</div>
<div class="gfg-sub-title">Neumorphism Login Form</div>
<div class="gfg-input-fields">
<div class="gfg-email">
<svg fill="#999" viewBox="0 0 1024 1024">
<path class="path1"
d="M896 307.2h-819.2c-42.347 0-76.8 34.453-76.8 76.8v460.8c0
42.349 34.453 76.8 76.8 76.8h819.2c42.349 0 76.8-34.451
76.8-76.8v-460.8c0-42.347-34.451-76.8-76.8-76.8zM896
358.4c1.514 0 2.99 0.158 4.434 0.411l-385.632 257.090c-14.862
9.907-41.938 9.907-56.802 0l-385.634-257.090c1.443-0.253
2.92-0.411 4.434-0.411h819.2zM896 870.4h-819.2c-14.115
0-25.6-11.485-25.6-25.6v-438.566l378.4 252.267c15.925
10.618 36.363 15.925 56.8 15.925s40.877-5.307
56.802-15.925l378.398-252.267v438.566c0 14.115-11.485
25.6-25.6 25.6z">
</path>
</svg>
<input type="email" placeholder="email" />
</div>
<div class="gfg-password">
<svg fill="#999" viewBox="0 0 1024 1024">
<path class="path1"
d="M742.4 409.6h-25.6v-76.8c0-127.043-103.
357-230.4-230.4-230.4s-230.4 103.357-230.4
230.4v76.8h-25.6c-42.347 0-76.8 34.453-76.8
76.8v409.6c0 42.347 34.453 76.8 76.8 76.8h512c42.347
0 76.8-34.453 76.8-76.8v-409.6c0-42.347-34.453-76.
8-76.8-76.8zM307.2 332.8c0-98.811 80.389-179.2
179.2-179.2s179.2 80.389 179.2 179.2v76.8h-358.4v-76.8zM768
896c0 14.115-11.485 25.6-25.6 25.6h-512c-14.115 0-25.6-11.
485-25.6-25.6v-409.6c0-14.115 11.485-25.6 25.6-25.6h512c14.
115 0 25.6 11.485 25.6 25.6v409.6z">
</path>
</svg>
<input type="password"
placeholder="password" />
</div>
</div>
<button class="gfg-button">Geeksforgeeks Signin</button>
<div class="gfg-link">
<a href="#"> Forgot password?</a> or <a href="#">Signup</a>
</div>
</div>
</body>
</html>
Output: