:root {
  --bg: #f5f7fa;
  --text: #333;
  --card: #fff;
  --border: #ccc;
  --button: #4e79a7;
  --button-hover: #355a7d;
}

body.dark {
  --bg: #1e1e1e;
  --text: #eee;
  --card: #2c2c2c;
  --border: #555;
  --button: #4e79a7;
  --button-hover: #638bba;
}

body {
  margin: 0;
  font-family: "Segoe UI", Roboto, sans-serif;
  background: var(--bg);
  color: var(--text);
  transition: background 0.3s ease, color 0.3s ease;
}

.container {
  max-width: 800px;
  margin: auto;
  padding: 30px 20px;
}

h1 {
  text-align: center;
  margin-bottom: 30px;
  color: var(--text);
}

.form {
  background: var(--card);
  padding: 20px;
  border-radius: 16px;
  box-shadow: 0 4px 10px rgba(0,0,0,0.08);
  display: flex;
  flex-direction: column;
  gap: 12px;
  transition: background 0.3s ease;
}

label {
  font-weight: bold;
}

input {
  padding: 10px;
  border: 1px solid var(--border);
  border-radius: 8px;
  font-size: 16px;
  background: white;
}

button {
  padding: 12px;
  font-size: 16px;
  background-color: var(--button);
  color: white;
  border: none;
  border-radius: 8px;
  cursor: pointer;
  transition: background-color 0.2s ease;
}

button:hover {
  background-color: var(--button-hover);
}

#plot {
  margin-top: 30px;
  width: 100%;
  height: 500px;
}