:root {
    /* Batman Theme - Default */
    --primary-color: #202020;
    --secondary-color: #3d3d3d;
    --accent-color: #ffb612;
    --text-color: #ffffff;
    --error-color: #ff3b30;
    --success-color: #34c759;
    --card-bg: rgba(30, 30, 30, 0.9);
    --input-bg: rgba(50, 50, 50, 0.8);
    --shadow-color: rgba(0, 0, 0, 0.5);
    --body-bg: url('https://wallpapercave.com/wp/wp6593228.jpg');
    --particle-color: rgba(255, 182, 18, 0.5);
  }
  
  /* Superman Theme */
  .superman-theme {
    --primary-color: #0033a0;
    --secondary-color: #0a4da3;
    --accent-color: #e51937;
    --text-color: #ffffff;
    --card-bg: rgba(0, 51, 160, 0.9);
    --input-bg: rgba(10, 77, 163, 0.8);
    --shadow-color: rgba(0, 0, 50, 0.5);
    --body-bg: url('https://wallpapercave.com/wp/wp2723910.jpg');
    --particle-color: rgba(229, 25, 55, 0.5);
  }
  
  /* Wonder Woman Theme */
  .wonder-woman-theme {
    --primary-color: #9e0b0f;
    --secondary-color: #b30e1d;
    --accent-color: #edb62d;
    --text-color: #ffffff;
    --card-bg: rgba(158, 11, 15, 0.9);
    --input-bg: rgba(179, 14, 29, 0.8);
    --shadow-color: rgba(100, 0, 0, 0.5);
    --body-bg: url('https://wallpapercave.com/wp/wp6040202.jpg');
    --particle-color: rgba(237, 182, 45, 0.5);
  }
  
  /* Flash Theme */
  .flash-theme {
    --primary-color: #ba0c2f;
    --secondary-color: #c30e34;
    --accent-color: #ffdd00;
    --text-color: #ffffff;
    --card-bg: rgba(186, 12, 47, 0.9);
    --input-bg: rgba(195, 14, 52, 0.8);
    --shadow-color: rgba(100, 0, 0, 0.5);
    --body-bg: url('https://wallpapercave.com/wp/wp5577493.jpg');
    --particle-color: rgba(255, 221, 0, 0.5);
  }
  
  /* Joker Theme */
  .joker-theme {
    --primary-color: #5e2180;
    --secondary-color: #752ba0;
    --accent-color: #4fe04b;
    --text-color: #ffffff;
    --card-bg: rgba(94, 33, 128, 0.9);
    --input-bg: rgba(117, 43, 160, 0.8);
    --shadow-color: rgba(50, 0, 80, 0.5);
    --body-bg: url('https://wallpapercave.com/wp/wp5696046.jpg');
    --particle-color: rgba(79, 224, 75, 0.5);
  }
  
  /* Base Styles */
  * {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'Montserrat', sans-serif;
  }
  
  body {
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    background-image: var(--body-bg);
    background-size: cover;
    background-position: center;
    background-attachment: fixed;
    overflow: hidden;
    transition: background-image 1s ease-in-out;
    perspective: 1000px;
  }
  
  body::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: radial-gradient(circle, transparent 20%, rgba(0, 0, 0, 0.7) 100%);
    z-index: -1;
  }
  
  .container {
    position: relative;
    width: 400px;
    height: 600px;
    z-index: 10;
    transform-style: preserve-3d;
    transition: transform 0.6s ease;
  }
  
  /* Card Styles */
  .card {
    width: 100%;
    height: 100%;
    position: relative;
    transform-style: preserve-3d;
    transition: transform 0.8s cubic-bezier(0.175, 0.885, 0.32, 1.275);
  }
  
  .card.flipped {
    transform: rotateY(180deg);
  }
  
  .card-inner {
    width: 100%;
    height: 100%;
    position: relative;
    transform-style: preserve-3d;
    transition: transform 0.8s cubic-bezier(0.175, 0.885, 0.32, 1.275);
  }
  
  .card-face {
    position: absolute;
    width: 100%;
    height: 100%;
    backface-visibility: hidden;
    background: var(--card-bg);
    border-radius: 20px;
    padding: 30px;
    box-shadow: 0 15px 35px var(--shadow-color);
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    overflow: hidden;
    transform-style: preserve-3d;
  }
  
  .sign-in-face {
    transform: rotateY(0deg);
    z-index: 2;
  }
  
  .sign-up-face {
    transform: rotateY(180deg);
    z-index: 1;
  }
  
  .card-face::before {
    content: '';
    position: absolute;
    top: -50%;
    left: -50%;
    width: 200%;
    height: 200%;
    background: radial-gradient(circle, var(--accent-color) 0%, transparent 20%);
    opacity: 0.05;
    animation: pulse 10s infinite linear;
    z-index: -1;
  }
  
  @keyframes pulse {
    0% {
      transform: scale(0.8);
      opacity: 0.05;
    }
    50% {
      transform: scale(1.2);
      opacity: 0.1;
    }
    100% {
      transform: scale(0.8);
      opacity: 0.05;
    }
  }
  
  /* Logo Styles */
  .logo {
    width: 80px;
    height: 80px;
    margin-bottom: 20px;
    transform: translateZ(30px);
    filter: drop-shadow(0 5px 15px rgba(0, 0, 0, 0.3));
  }
  
  .dc-logo {
    width: 100%;
    height: 100%;
    animation: float 4s ease-in-out infinite;
  }
  
  @keyframes float {
    0%, 100% {
      transform: translateY(0);
    }
    50% {
      transform: translateY(-10px);
    }
  }
  
  /* Heading Styles */
  h2 {
    color: var(--text-color);
    margin-bottom: 30px;
    font-weight: 600;
    font-size: 28px;
    text-transform: uppercase;
    letter-spacing: 2px;
    transform: translateZ(20px);
    text-shadow: 0 2px 5px rgba(0, 0, 0, 0.3);
  }
  
  /* Form Styles */
  .form {
    width: 100%;
    transform: translateZ(10px);
  }
  
  .form-group {
    position: relative;
    margin-bottom: 25px;
  }
  
  .form-input {
    width: 100%;
    padding: 15px 15px 15px 45px;
    border: none;
    border-radius: 10px;
    background: var(--input-bg);
    color: var(--text-color);
    font-size: 16px;
    transition: all 0.3s;
    box-shadow: 0 5px 15px rgba(0, 0, 0, 0.1);
    outline: none;
  }
  
  .form-input:focus {
    box-shadow: 0 5px 15px rgba(0, 0, 0, 0.2);
  }
  
  .form-label {
    position: absolute;
    left: 45px;
    top: 15px;
    color: #aaa;
    font-size: 16px;
    pointer-events: none;
    transition: 0.3s ease;
  }
  
  .form-input:focus ~ .form-label,
  .form-input:valid ~ .form-label {
    top: -10px;
    left: 20px;
    font-size: 12px;
    color: var(--accent-color);
    background: var(--card-bg);
    padding: 0 8px;
    border-radius: 5px;
  }
  
  .input-icon {
    position: absolute;
    left: 15px;
    top: 17px;
    color: #aaa;
    font-size: 18px;
    transition: 0.3s;
  }
  
  .form-input:focus ~ .input-icon {
    color: var(--accent-color);
  }
  
  .remember-forgot {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 20px;
    color: var(--text-color);
    font-size: 14px;
  }
  
  .checkbox-container {
    display: flex;
    align-items: center;
    cursor: pointer;
  }
  
  .checkbox-container input {
    opacity: 0;
    width: 0;
    height: 0;
  }
  
  .checkmark {
    position: relative;
    display: inline-block;
    width: 18px;
    height: 18px;
    margin-right: 8px;
    background: var(--input-bg);
    border-radius: 4px;
  }
  
  .checkbox-container input:checked ~ .checkmark:after {
    content: '';
    position: absolute;
    top: 3px;
    left: 6px;
    width: 5px;
    height: 10px;
    border: solid var(--accent-color);
    border-width: 0 2px 2px 0;
    transform: rotate(45deg);
  }
  
  .forgot-password {
    color: var(--accent-color);
    text-decoration: none;
    transition: all 0.3s;
  }
  
  .forgot-password:hover {
    text-decoration: underline;
  }
  
  .submit-btn {
    width: 100%;
    padding: 15px;
    background: var(--accent-color);
    color: var(--primary-color);
    border: none;
    border-radius: 10px;
    font-size: 16px;
    font-weight: 600;
    cursor: pointer;
    display: flex;
    justify-content: center;
    align-items: center;
    transition: all 0.3s;
    box-shadow: 0 5px 15px rgba(0, 0, 0, 0.2);
    text-transform: uppercase;
    letter-spacing: 1px;
    margin-bottom: 20px;
  }
  
  .submit-btn:hover {
    transform: translateY(-3px);
    box-shadow: 0 8px 20px rgba(0, 0, 0, 0.3);
  }
  
  .submit-btn:active {
    transform: translateY(1px);
  }
  
  .submit-btn span {
    margin-right: 10px;
  }
  
  /* Social Login */
  .social-login {
    width: 100%;
    text-align: center;
    margin-bottom: 20px;
  }
  
  .social-login p {
    color: var(--text-color);
    margin-bottom: 15px;
    font-size: 14px;
    position: relative;
  }
  
  .social-login p::before,
  .social-login p::after {
    content: '';
    position: absolute;
    top: 50%;
    width: 60px;
    height: 1px;
    background: rgba(255, 255, 255, 0.3);
  }
  
  .social-login p::before {
    left: 20px;
  }
  
  .social-login p::after {
    right: 20px;
  }
  
  .social-icons {
    display: flex;
    justify-content: center;
    gap: 15px;
  }
  
  .social-btn {
    width: 45px;
    height: 45px;
    border-radius: 50%;
    border: none;
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 18px;
    cursor: pointer;
    transition: all 0.3s;
    color: white;
  }
  
  .social-btn:hover {
    transform: translateY(-3px);
    box-shadow: 0 5px 15px rgba(0, 0, 0, 0.3);
  }
  
  .google {
    background: #DB4437;
  }
  
  .facebook {
    background: #4267B2;
  }
  
  .twitter {
    background: #1DA1F2;
  }
  
  .switch-text {
    color: var(--text-color);
    font-size: 14px;
    margin-top: 20px;
  }
  
  .switch-btn {
    color: var(--accent-color);
    text-decoration: none;
    font-weight: 600;
    transition: all 0.3s;
    cursor: pointer;
  }
  
  .switch-btn:hover {
    text-decoration: underline;
  }
  
  /* Theme Switcher */
  .theme-switcher {
    position: fixed;
    top: 20px;
    right: 20px;
    display: flex;
    gap: 10px;
    z-index: 100;
  }
  
  .theme-btn {
    background: rgba(0, 0, 0, 0.6);
    color: white;
    border: none;
    border-radius: 30px;
    padding: 8px 15px;
    display: flex;
    align-items: center;
    gap: 8px;
    cursor: pointer;
    transition: all 0.3s;
    font-size: 14px;
    box-shadow: 0 3px 10px rgba(0, 0, 0, 0.2);
  }
  
  .theme-btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 5px 15px rgba(0, 0, 0, 0.3);
  }
  
  .theme-btn.active {
    background: var(--accent-color);
    color: var(--primary-color);
  }
  
  /* Particles */
  .particles-container {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    pointer-events: none;
    z-index: 1;
    overflow: hidden;
  }
  
  .particles {
    width: 100%;
    height: 100%;
    position: relative;
  }
  
  /* Animation for 3D card movement */
  @keyframes cardFloat {
    0%, 100% {
      transform: translateZ(0) rotateX(0deg) rotateY(0deg);
    }
    25% {
      transform: translateZ(10px) rotateX(2deg) rotateY(-2deg);
    }
    50% {
      transform: translateZ(20px) rotateX(-2deg) rotateY(2deg);
    }
    75% {
      transform: translateZ(10px) rotateX(2deg) rotateY(-2deg);
    }
  }
  
  .container {
    animation: cardFloat 8s infinite ease-in-out;
  }
  
  /* Responsive styles */
  @media (max-width: 450px) {
    .container {
      width: 90%;
      height: 580px;
    }
    
    .card-face {
      padding: 20px;
    }
    
    .logo {
      width: 60px;
      height: 60px;
    }
    
    h2 {
      font-size: 24px;
    }
    
    .form-input {
      padding: 12px 12px 12px 40px;
    }
    
    .form-label {
      left: 40px;
      top: 12px;
    }
    
    .input-icon {
      left: 12px;
      top: 14px;
    }
    
    .social-login p::before,
    .social-login p::after {
      width: 40px;
    }
    
    .theme-switcher {
      top: 10px;
      right: 10px;
      flex-wrap: wrap;
      justify-content: flex-end;
      max-width: 200px;
    }
    
    .theme-btn {
      padding: 5px 10px;
      font-size: 12px;
    }
  }