HTML

CSS

JS

* {
     box-sizing: border-box;
}

body{
    background-image: linear-gradient(19deg, #21D4FD 0%, #B721FF 100%);
}

.box {
     display: flex;
     align-items: center;
     justify-content: center;
     height: 100vh;
}

.login-form {
     min-width: 250px;
     max-width: 400px;
     border-radius: 24px;
     padding: 15px;
     background: #fff;
}

.login-form h1 {
     text-align: center;
     font-size: 2.5rem;
     margin-top: 35px;
}

.login-form input[type = "text"] {
     margin-top: 30px;
}

.login-form input[type = "password"] {
     margin-top: 10px;
}

input {
     outline: none;
}

.links {
     margin-top: 10px;
     display: flex;
     flex-wrap: wrap;
     flex-direction: row;
}

.links > a:first-of-type {
     margin-right: 5px;
}

.login-form input[type = "submit"] {
     background-color: #E0E0E0;
     background-image: linear-gradient(19deg, #21D4FD 0%, #B721FF 100%);
     width: 100%;
     color: white;
     border: none;
     margin-top: 35px;
     cursor: pointer;
     padding: 10px;
     font-family: 'Raleway', sans-seriff;
     font-size: 1.3rem;
     font-weight: bold;
     border-radius: 24px;
     transition: 0.25s;
}

.login-form input[type = "submit"]:hover {
     opacity: 0.8;
}

.login-form input[type = "text"]:focus, .login-form input[type = "password"]:focus {
     border: 2px #21D4FD solid;
}

.login-form input[type = "text"], .login-form input[type = "password"] {
     width: 100%;
     border: none;
     border-radius: 24px;
     font-size: 1rem;
     font-family: 'Raleway', sans-seriff;
     background-color: gainsboro;
     padding: 15px;
}

Login Form with Gradient Button

A simple login form with a gradient button and basic validation for username and password.

You can remove CSS lines 5-7 if you do not want a gradient background. You can also change CSS line 74 if you want a different color for form validation.