body {
  font-family: Arial, sans-serif;
  background: #f8f9fa;
  color: #333;
  display: flex;
  justify-content: center;
  padding: 2rem;
}

.container {
  background: #fff;
  padding: 2rem;
  border-radius: 12px;
  box-shadow: 0 4px 12px rgba(0,0,0,0.1);
  max-width: 600px;
  width: 100%;
}

h1 {
  text-align: center;
  margin-bottom: 1rem;
}

form {
  display: grid;
  grid-template-columns: 1fr 1fr; /* two equal columns */
  gap: 1rem;
}

.child-column {
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

label {
  display: flex;
  flex-direction: column;
  font-size: 0.9rem;
}

input, select, button {
  padding: 0.5rem;
  margin-top: 0.3rem;
  border: 1px solid #ccc;
  border-radius: 6px;
}

button {
  grid-column: span 2;
  background: #007bff;
  color: white;
  font-weight: bold;
  cursor: pointer;
  transition: background 0.3s;
}

button:hover {
  background: #0056b3;
}

/* Chart */
.chart-wrapper {
  margin-top: 2rem;
  text-align: center;
}

canvas {
  max-width: 600px;
  max-height: 400px;
}

/* Toggle switch */
.unit-toggle {
  grid-column: span 2;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  margin-top: 0.5rem;
}

.switch {
  position: relative;
  display: inline-block;
  width: 50px;
  height: 24px;
}

.switch input {display:none;}

.slider {
  position: absolute;
  cursor: pointer;
  top: 0; left: 0; right: 0; bottom: 0;
  background-color: #ccc;
  transition: .4s;
  border-radius: 24px;
}

.slider:before {
  position: absolute;
  content: "";
  height: 18px;
  width: 18px;
  left: 3px;
  bottom: 3px;
  background-color: white;
  transition: .4s;
  border-radius: 50%;
}

input:checked + .slider {
  background-color: #007bff;
}

input:checked + .slider:before {
  transform: translateX(26px);
}