问Uncaught :无法读取空角的属性'addEventListener‘

EN

const signUpButton = document.getElementById('signUp');
const signInButton = document.getElementById('signIn');
const container = document.getElementById('container');

signUpButton.addEventListener('click', () => {
  container.classList.add('right-panel-active');
});

signInButton.addEventListener('click', () => {
  container.classList.remove('right-panel-active');
});

<!-- main section  -->
<div class="container container text-center" id="container">
  <div class="form-container sign-up-container">
    <!-- Sign Up form code goes here -->
    <form action="#">
      <h1 class="text-center">Create Account</h1>
      <div class="social-container">
        <a href="#" class="social"><i class="fab fa-facebook-f"></i></a>
        <a href="#" class="social"><i class="fab fa-google-plus-g"></i></a>
      </div>
      <span>or use your email for registration</span>
      <input type="text" class="form-control custInp" placeholder="Name" />
      <input type="email" class="form-control custInp" placeholder="Email" />
      <input type="password" class="pse" placeholder="Password" />
      <button>Sign Up</button>
    </form>
  </div>
  <div class="form-container sign-in-container">
    <!-- Sign In form code goes here -->
    <form action="#">
      <h1>Sign in</h1>
      <div class="social-container">
        <a href="#" class="social"><i class="fab fa-facebook-f"></i></a>
        <a href="#" class="social"><i class="fab fa-google-plus-g"></i></a>
        <a href="#" class="social"><i class="fab fa-linkedin-in"></i></a>
      </div>
      <span>or use your account</span>
      <input type="email" class="form-control custInp" placeholder="Email" />
      <input type="password" class="form-control custInp" placeholder="Password" />
      <a href="#">Forgot your password?</a>
      <button>Sign In</button>
    </form>

  </div>
  <div class="overlay-container">
    <!-- The overlay code goes here -->
    <div class="overlay">
      <div class="overlay-panel overlay-left">
        <h1>Welcome Back!</h1>
        <p>
          To keep connected with us please login with your personal info
        </p>
        <button class="ghost" id="signIn">Sign In</button>
      </div>
      <div class="overlay-panel overlay-right">
        <h1>Hello, Friend!</h1>
        <p>Enter your personal details and start journey with us</p>
        <button class="ghost" id="signUp">Sign Up</button>
      </div>
    </div>
  </div>
</div>
<!-- main section  -->