:root {
  --body-bg-color: #f4f4f4;
  --form-bg-color: #fff;
  --primary-color: #007bff;
  --primary-color-darker: #0056b3;
  --text-color-dark: #333;
  --border-color: #ccc;
  --border-radius-small: 5px;
  --border-radius-medium: 10px;
  --box-shadow-color: rgba(0, 0, 0, 0.1);
  --input-padding: 12px;
  --form-padding-desktop: 30px;
  --form-padding-mobile: 20px;
  --form-margin-mobile: 10px;
  --input-border-width: 1px;
  --input-margin-bottom: 10px;
  --label-margin-bottom: 8px;
  --paragraph-margin-bottom: 20px;
  --button-padding-desktop-vertical: 12px;
  --button-padding-desktop-horizontal: 20px;
  --button-padding-mobile: 15px;
  --font-size-base: 16px;
  --font-size-large: 18px;
  --textarea-height: 150px;
  --form-max-width: 500px;
  --transition-duration: 0.3s;
  --invalid-color: #dc3545;
  --valid-color: #28a745;
  --focus-shadow-color-primary: rgba(0, 123, 255, 0.5);
  --focus-shadow-color-invalid: rgba(220, 53, 69, 0.5);
}

@media (max-width: 480px) {
  form {
    padding: var(--form-padding-mobile);
    margin: var(--form-margin-mobile);
  }

  button[type="submit"] {
    width: 100%;
    padding: var(--button-padding-mobile);
    font-size: var(--font-size-large);
  }
}

body {
  font-family: sans-serif;
  background-color: var(--body-bg-color);
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  margin: 0;
  padding: var(--form-padding-mobile); /* Using mobile padding for body as well for consistency on small screens */
}

form {
  background-color: var(--form-bg-color);
  padding: var(--form-padding-desktop);
  border-radius: var(--border-radius-medium);
  box-shadow: 0 5px 15px var(--box-shadow-color);
  width: 100%;
  max-width: var(--form-max-width);
}

p {
  margin-bottom: var(--paragraph-margin-bottom);
}

label {
  display: block;
  margin-bottom: var(--label-margin-bottom);
  font-weight: bold;
  color: var(--text-color-dark);
}

input[type="text"],
input[type="email"],
textarea {
  width: 100%;
  padding: var(--input-padding);
  border: var(--input-border-width) solid var(--border-color);
  border-radius: var(--border-radius-small);
  font-size: var(--font-size-base);
  box-sizing: border-box;
  margin-bottom: var(--input-margin-bottom);
}

textarea {
  height: var(--textarea-height);
  resize: vertical;
}

button[type="submit"] {
  background-color: var(--primary-color);
  color: white;
  padding: var(--button-padding-desktop-vertical) var(--button-padding-desktop-horizontal);
  border: none;
  border-radius: var(--border-radius-small);
  cursor: pointer;
  font-size: var(--font-size-base);
  transition: background-color var(--transition-duration) ease;
}

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

input[type="text"]:focus,
input[type="email"]:focus,
textarea:focus {
  outline: none;
  border-color: var(--primary-color);
  box-shadow: 0 0 5px var(--focus-shadow-color-primary);
}

/* Existing CSS remains the same up to the validation styles */

/* Replace existing :invalid and :valid styles with the following */
input:invalid:not(:placeholder-shown),
textarea:invalid:not(:placeholder-shown) {
  border-color: var(--invalid-color);
}

input:valid:not(:placeholder-shown),
textarea:valid:not(:placeholder-shown) {
  border-color: var(--valid-color);
}

input:invalid:not(:placeholder-shown):focus,
textarea:invalid:not(:placeholder-shown):focus {
  box-shadow: 0 0 5px var(--focus-shadow-color-invalid);
}

.hidden {
  display: none;
 }
 
 .required-star {
    color: red;
    font-size: 1.2em;
    margin-left: 0.2em;
}