JSFiddle - React, Tailwind, and code Playground

HTML

<form id='myForm' method='post' action='login.php'>
    <input type='text' placeholder='Username'/>
    <input type='password' placeholder='Password'/>
    <button type='submit'>Anmelden</button>
</form>

CSS

form{
    display: block;
    margin: 0 auto;
    padding: 10px;
    max-width: 300px;
}

input{
    display: block;
    margin: 2px 0;
    padding: 3px;
    width: 100%;
}

JavaScript

var form = document.getElementById('myForm');
form.addEventListener('submit', function(e){
    alert('Ajax-Request implementieren..');
    e.preventDefault();
});