:root {
  --background: #0d1117;
  --text: #c9d1d9;
  --accent: #58a6ff;
  --error: #ff7b72;
  --success: #7ee787;
}

* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
  background-color: var(--background);
  color: var(--text);
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 100vh;
  padding: 2rem;
}

main {
  background-color: #161b22;
  padding: 2.5rem 3rem;
  border-radius: 12px;
  box-shadow: 0 0 20px rgba(0, 0, 0, 0.5);
  max-width: 450px;
  width: 100%;
  text-align: center;
}

h1 {
  margin-bottom: 1.2rem;
  font-size: 1.8rem;
}

label {
  display: block;
  margin-bottom: 0.5rem;
  font-size: 1.1rem;
}

#user-input {
  width: 100%;
  padding: 0.75rem;
  font-size: 1rem;
  border: none;
  border-radius: 6px;
  margin-bottom: 1rem;
  background-color: #21262d;
  color: var(--text);
}

.buttons {
  display: flex;
  gap: 1rem;
  justify-content: center;
  margin-bottom: 1.2rem;
}

button {
  padding: 0.6rem 1.5rem;
  font-size: 1rem;
  border: none;
  border-radius: 6px;
  cursor: pointer;
  transition: background 0.2s ease;
}

#check-btn {
  background-color: var(--accent);
  color: #000;
}

#check-btn:hover {
  background-color: #79c0ff;
}

#clear-btn {
  background-color: #484f58;
  color: #fff;
}

#clear-btn:hover {
  background-color: #6e7681;
}

#results-div {
  font-size: 1.1rem;
  word-break: break-word;
}

#results-div.valid {
  color: var(--success);
}

#results-div.invalid {
  color: var(--error);
}