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

body {
  font-family: "Nunito", sans-serif;
  min-height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  background: linear-gradient(135deg, #0f0f1f, #1a1a3e);
}

#card {
  width: 420px;
  animation: fadeIn 0.4s ease;
}

@keyframes fadeIn {
  from {
    opacity: 0;
  }
  to {
    opacity: 1;
  }
}

#upper-container {
  background-color: #1e1b4b;
  padding: 2rem;
  border-radius: 12px 12px 0 0;
  text-align: center;
  color: white;
}

h1 {
  font-size: 1.4rem;
  font-weight: 800;
  margin-bottom: 1.2rem;
  color: #ffffff;
}

input {
  padding: 0.6rem;
  font-size: 1.2rem;
  font-family: "Nunito", sans-serif;
  background-color: #0f0f0f;
  color: white;
  border: 2px solid #2d2a6e;
  border-radius: 8px;
  text-align: center;
  outline: none;
  transition: border-color 0.3s ease;
}

input:focus {
  border-color: #7e59e4;
  box-shadow: 0 0 10px rgba(126, 89, 228, 0.4);
}

#alert-msg {
  color: #f87171;
  font-size: 0.85rem;
  min-height: 1.2rem;
  margin-top: 0.4rem;
}

button {
  margin-top: 0.8rem;
  padding: 0.6rem 2rem;
  background-color: #5b4de8;
  color: white;
  font-family: "Nunito", sans-serif;
  font-weight: 700;
  font-size: 1rem;
  border: none;
  border-radius: 8px;
  cursor: pointer;
  transition:
    background-color 0.3s ease,
    transform 0.15s ease;
}

button:hover {
  background-color: #7e59e4;
  transform: translateY(-2px);
  box-shadow: 0 0 14px rgba(126, 89, 228, 0.4);
}

button:active {
  transform: translateY(0);
}

#lower-container {
  background-color: #161616;
  border-radius: 0 0 12px 12px;
  padding: 1.5rem;
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.equation-area {
  background-color: #1a1a1a;
  border-radius: 8px;
  padding: 1rem 1.2rem;
  text-align: center;
  transition:
    transform 0.2s ease,
    box-shadow 0.2s ease;
  box-shadow: 0 4px 16px rgba(91, 77, 232, 0.3);
}

.equation-area:hover {
  transform: translateY(-2px);
  box-shadow: 0 4px 16px rgba(91, 77, 232, 0.3);
}

.equation-area h3 {
  font-size: 1rem;
  font-weight: 800;
  margin-bottom: 0.4rem;
  color: #a89df0;
}

.equation-area p {
  font-size: 0.85rem;
  color: #888;
}