تمرین shortcode

سلام و درود بر استاد عزیزم. تمرین بخش shortcode 

<?php
/*
  Plugin Name:       Login Shortcode
  Plugin URI:        https://picomedia.ir
  Description:       The First Plugin . This is a initial Version.
  Version:           1.0.0
  Requires at least: 5.2
  Requires PHP:      7.2
  Author:            Pouya Pazhoohandeh
  Author URI:        https://picomedia.ir
  License:           GPL v2 or later
  License URI:       https://www.gnu.org/licenses/gpl-2.0.html
  Update URI:        https://picomedia.ir
  Domain Path:       /languages/
 */
function login_page()
{
    return '
   <style> 
   body {
    box-sizing: border-box;
    direction: ltr;
    height: auto;
    width: 90%;
    margin: 10px auto;
  }
  
  .form {
    background-color: #15172b;
    border-radius: 20px;
    box-sizing: border-box;
    height: 500px;
    padding: 20px;
    width: 320px;
  }
  
  .title {
    color: #eee;
    font-family: sans-serif;
    font-size: 36px;
    font-weight: 600;
    margin-top: 30px;
  }
  
  .subtitle {
    color: #eee;
    font-family: sans-serif;
    font-size: 16px;
    font-weight: 600;
    margin-top: 10px;
  }
  .subtitle2 {
    color: #eee;
    font-family: sans-serif;
    font-size: 12px;
    font-weight: 600;
    margin-top: 10px;
  }
  
  
  .input-container {
    height: 50px;
    position: relative;
    width: 100%;
  }
  
  .ic1 {
    margin-top: 40px;
  }
  
  .ic2 {
    margin-top: 30px;
  }
  
  .input {
    background-color: #303245;
    border-radius: 12px;
    border: 0;
    box-sizing: border-box;
    color: #eee;
    font-size: 18px;
    height: 100%;
    outline: 0;
    padding: 4px 20px 0;
    width: 100%;
  }
  
  .cut {
    background-color: #15172b;
    border-radius: 10px;
    height: 20px;
    left: 20px;
    position: absolute;
    top: -20px;
    transform: translateY(0);
    transition: transform 200ms;
    width: 76px;
  }
  
  .cut-short {
    width: 50px;
  }
  
  .input:focus ~ .cut,
  .input:not(:placeholder-shown) ~ .cut {
    transform: translateY(8px);
  }
  
  .placeholder {
    color: #65657b;
    font-family: sans-serif;
    left: 20px;
    line-height: 14px;
    pointer-events: none;
    position: absolute;
    transform-origin: 0 50%;
    transition: transform 200ms, color 200ms;
    top: 20px;
  }
  
  .input:focus ~ .placeholder,
  .input:not(:placeholder-shown) ~ .placeholder {
    transform: translateY(-30px) translateX(10px) scale(0.75);
  }
  
  .input:not(:placeholder-shown) ~ .placeholder {
    color: #808097;
  }
  
  .input:focus ~ .placeholder {
    color: #dc2f55;
  }
  
  .submit {
    background-color: #08d;
    border-radius: 12px;
    border: 0;
    box-sizing: border-box;
    color: #eee;
    cursor: pointer;
    font-size: 18px;
    height: 50px;
    margin-top: 38px;
    // outline: 0;
    text-align: center;
    width: 100%;
  }
  
  .submit:active {
    background-color: #06b;
  }
    </style>
   <div class="form">
   <div class="title">Login Form</div>
   <div class="subtitle">By Pouya Pazhoohandeh</div>
   <div class="subtitle2"> with ♥ for 7Learn </div>
   <div class="input-container ic1">
     <input id="username" class="input" type="text" placeholder=" " />
     <div class="cut"></div>
     <label for="Username" class="placeholder">Username</label>
   </div>
   <div class="input-container ic2">
     <input id="password" class="input" type="text" placeholder=" " />
     <div class="cut"></div>
     <label for="password" class="placeholder">Password</label>
   </div>
   <button type="text" class="submit">submit</button>
 </div>
   ';
}

add_shortcode("login_page", "login_page");