W3School TIY Editor

<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1">
<style>
body {font-family: Arial, Helvetica, sans-serif;}

/* 全宽输入框 */
input[type=text], input[type=password] {
  width: 100%;
  padding: 12px 20px;
  margin: 8px 0;
  display: inline-block;
  border: 1px solid #ccc;
  box-sizing: border-box;
}

/* 为所有按钮设置样式 */
button {
  background-color: #04AA6D;
  color: white;
  padding: 14px 20px;
  margin: 8px 0;
  border: none;
  cursor: pointer;
  width: 100%;
}

button:hover {
  opacity: 0.8;
}

/* 取消按钮的额外样式 */
.cancelbtn {
  width: auto;
  padding: 10px 18px;
  background-color: #f44336;
}

/* 居中图像并定位关闭按钮 */
.imgcontainer {
  text-align: center;
  margin: 24px 0 12px 0;
  position: relative;
}

img.avatar {
  width: 40%;
  border-radius: 50%;
}

.container {
  padding: 16px;
}

span.psw {
  float: right;
  padding-top: 16px;
}

/* 模态框 (背景) */
.modal {
  display: none; /* 默认隐藏 */
  position: fixed; /* 固定位置 */
  z-index: 1; /* 高于其他元素 */
  left: 0;
  top: 0;
  width: 100%; /* 全宽 */
  height: 100%; /* 全高 */
  overflow: auto; /* 必要时启用滚动 */
  background-color: rgb(0,0,0); /* 备用颜色 */
  background-color: rgba(0,0,0,0.4); /* 黑色带透明度 */
  padding-top: 60px;
}

/* 模态框内容/盒子 */
.modal-content {
  background-color: #fefefe;
  margin: 5% auto 15% auto; /* 从顶部 5%，底部 15% 居中 */
  border: 1px solid #888;
  width: 80%; /* 根据屏幕大小可多可少 */
}

/* 关闭按钮 (x) */
.close {
  position: absolute;
  right: 25px;
  top: 0;
  color: #000;
  font-size: 35px;
  font-weight: bold;
}

.close:hover,
.close:focus {
  color: red;
  cursor: pointer;
}

/* 添加缩放动画 */
.animate {
  -webkit-animation: animatezoom 0.6s;
  animation: animatezoom 0.6s
}

@-webkit-keyframes animatezoom {
  from {-webkit-transform: scale(0)} 
  to {-webkit-transform: scale(1)}
}
  
@keyframes animatezoom {
  from {transform: scale(0)} 
  to {transform: scale(1)}
}

/* 在极小屏幕上改变 span 和取消按钮的样式 */
@media screen and (max-width: 300px) {
  span.psw {
     display: block;
     float: none;
  }
  .cancelbtn {
     width: 100%;
  }
}
</style>
</head>
<body>

<h2>模态登录表单</h2>

<button onclick="document.getElementById('id01').style.display='block'" style="width:auto;">Login</button>

<div class="container">
      <label for="uname"><b>Username</b></label>
      <input type="text" placeholder="Enter Username" name="uname" required>

<label for="psw"><b>Password</b></label>
      <input type="password" placeholder="Enter Password" name="psw" required>
        
      <button type="submit">Login</button>
      <label>
        <input type="checkbox" checked="checked" name="remember"> Remember me
      </label>
    </div>

<div class="container" style="background-color:#f1f1f1">
      <button type="button" onclick="document.getElementById('id01').style.display='none'" class="cancelbtn">Cancel</button>
      <span class="psw">Forgot <a href="#">password?</a></span>
    </div>
  </form>
</div>

// 当用户单击模态之外的任何位置时，将其关闭 
window.onclick = function(event) {
  if (event.target == modal) {
    modal.style.display = "none";
  }
}
</script>

</body>
</html>