Click to jump out and drag the pop-up window

effect :

Code

  * {
    
            margin: 0;
            padding: 0;
        }
        
        .login_bg {
    
            display: none;
            position: absolute;
            width: 100%;
            height: 100%;
            background-color: rgba(0, 0, 0, 0.6);
            z-index: 1;
        }
        
        h1 {
    
            text-align: center;
        }
        
        .login_box {
    
            display: none;
            position: fixed;
            top: 50%;
            left: 50%;
            transform: translateX(-50%) translateY(-50%);
            text-align: center;
            width: 400px;
            height: 200px;
            background-color: pink;
            z-index: 2;
        }

 <div id='bg' class="login_bg"></div>
    <h1> Click to pop up the login box </h1>
    <div class="login_box">
        <h3> Member login </h3>
        <div>  user name :<input type="text" value=" Please enter a user name "></div>
        <div>  password :<input type="password" value=" Please enter the login password "></div>
        <button class="link"> Login member </button>
        <button class="close"> close </button>

 var login_box = document.querySelector('.login_box');
            var mask = document.querySelector('.login_bg');
            var h1 = document.querySelector('h1');
            var close = document.querySelector('.close');
            var link = document.querySelector('.link');
            var h3 = document.querySelector('h3');
            h1.addEventListener('click', function() {
    
                login_box.style.display = 'block';
                mask.style.display = 'block';
            });
            close.addEventListener('click', function() {
    
                login_box.style.display = 'none';
                mask.style.display = 'none';
            });
            //  Get the mouse coordinates in the box 
            h3.addEventListener('mousedown', function(e) {
    
                var x = e.pageX - login_box.offsetLeft;
                var y = e.pageY - login_box.offsetTop;
                //  Coordinates from the border to the edge of the document 
                document.addEventListener('mousemove', fn);

                function fn(e) {
    
                    login_box.style.left = e.pageX - x + 'px';
                    login_box.style.top = e.pageY - y + 'px';
                }
                //  Mouse movement event removal 
                document.addEventListener('mouseup', function() {
    
                    document.removeEventListener('mousemove', fn);
                });
            });