:root {
  --background-color-light: #f0f2f5;
  --text-color-light: #333;
  --card-bg-light: #ffffff;
  --input-bg-light: #ffffff;
  --border-color-light: #ddd;
  --primary-color: #007bff;
  --primary-hover: #0056b3;

  --background-color-dark: #1a1a1a;
  --text-color-dark: #f0f2f5;
  --card-bg-dark: #2c2c2c;
  --input-bg-dark: #3a3a3a;
  --border-color-dark: #444;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  margin: 0;
  background-color: var(--background-color-light);
  color: var(--text-color-light);
  transition: background-color 0.3s, color 0.3s;
}

body.dark-mode {
  background-color: var(--background-color-dark);
  color: var(--text-color-dark);
}

.container {
  background-color: var(--card-bg-light);
  padding: 2rem;
  border-radius: 12px;
  box-shadow: 0 4px 20px rgba(0, 0, 0, 0.1);
  width: 100%;
  max-width: 450px;
  transition: background-color 0.3s;
}

body.dark-mode .container {
  background-color: var(--card-bg-dark);
  box-shadow: 0 4px 20px rgba(0, 0, 0, 0.4);
}

h1 {
  text-align: center;
  margin-bottom: 1.5rem;
  font-size: 1.8rem;
}

.form-group {
  margin-bottom: 1.2rem;
}

label {
  display: block;
  margin-bottom: 0.5rem;
  font-weight: 600;
  font-size: 0.9rem;
}

input, textarea {
  width: 100%;
  padding: 0.8rem;
  border: 1px solid var(--border-color-light);
  border-radius: 6px;
  background-color: var(--input-bg-light);
  color: inherit;
  font-family: inherit;
  font-size: 1rem;
  box-sizing: border-box;
  transition: border-color 0.2s, background-color 0.3s;
}

body.dark-mode input, 
body.dark-mode textarea {
  border-color: var(--border-color-dark);
  background-color: var(--input-bg-dark);
}

input:focus, textarea:focus {
  outline: none;
  border-color: var(--primary-color);
}

button[type="submit"] {
  width: 100%;
  padding: 0.8rem;
  background-color: var(--primary-color);
  color: white;
  border: none;
  border-radius: 6px;
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  transition: background-color 0.2s;
}

button[type="submit"]:hover {
  background-color: var(--primary-hover);
}

#theme-toggle {
  position: fixed;
  top: 20px;
  right: 20px;
  padding: 8px 12px;
  border: 1px solid var(--border-color-light);
  background: var(--card-bg-light);
  color: var(--text-color-light);
  border-radius: 5px;
  cursor: pointer;
  font-size: 0.8rem;
  transition: all 0.3s;
}

body.dark-mode #theme-toggle {
  border-color: var(--border-color-dark);
  background: var(--card-bg-dark);
  color: var(--text-color-dark);
}