:root {
  --bg: #0f1221;
  --panel: #171b2e;
  --accent: #7c6cf6;
  --accent-light: #a89bff;
  --text: #e8e8f2;
  --muted: #9a9cc0;
  --border: #2a2f4a;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  font-family: "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  background: linear-gradient(180deg, var(--bg), #0a0c16);
  color: var(--text);
  min-height: 100vh;
}

header {
  text-align: center;
  padding: 2.5rem 1rem 1rem;
}

header h1 {
  margin: 0;
  font-size: 2.4rem;
  letter-spacing: 1px;
  color: var(--accent-light);
}

.subtitle {
  color: var(--muted);
  margin-top: 0.4rem;
}

main {
  max-width: 720px;
  margin: 0 auto;
  padding: 1rem 1.2rem 3rem;
}

form {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 1.5rem;
  display: flex;
  flex-direction: column;
  gap: 0.9rem;
}

label {
  font-size: 0.9rem;
  color: var(--muted);
  margin-bottom: 0.3rem;
  display: block;
}

input[type="text"] {
  width: 100%;
  padding: 0.7rem 0.9rem;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: #10132299;
  color: var(--text);
  font-size: 1.05rem;
}

input[type="text"]:focus {
  outline: 2px solid var(--accent);
}

.bounds-toggle label {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  color: var(--text);
  font-size: 0.95rem;
}

.bounds {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1rem;
}

button[type="submit"] {
  background: var(--accent);
  color: white;
  border: none;
  padding: 0.8rem 1rem;
  border-radius: 8px;
  font-size: 1.05rem;
  font-weight: 600;
  cursor: pointer;
  transition: background 0.15s;
}

button[type="submit"]:hover {
  background: var(--accent-light);
}

.examples {
  margin-top: 1.2rem;
  color: var(--muted);
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  align-items: center;
}

.example {
  background: #1d2340;
  color: var(--accent-light);
  border: 1px solid var(--border);
  padding: 0.35rem 0.7rem;
  border-radius: 20px;
  cursor: pointer;
  font-size: 0.85rem;
}

.example:hover {
  background: #272e52;
}

#result {
  margin-top: 1.5rem;
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 1.5rem;
}

#result h2 {
  margin-top: 0;
  color: var(--accent-light);
}

.step {
  border-left: 3px solid var(--accent);
  padding: 0.5rem 0 0.5rem 0.9rem;
  margin-bottom: 0.9rem;
}

.step .step-text {
  color: var(--muted);
  font-size: 0.92rem;
  margin-bottom: 0.3rem;
}

.step .step-math {
  font-size: 1.1rem;
  overflow-x: auto;
}

.final-box {
  margin-top: 1.2rem;
  padding: 1rem;
  background: #11142499;
  border-radius: 10px;
  border: 1px solid var(--border);
}

.final-box .label {
  color: var(--muted);
  font-size: 0.85rem;
  margin-bottom: 0.4rem;
}

.katex-display-wrap {
  overflow-x: auto;
}

#error {
  margin-top: 1.2rem;
  background: #3a1620;
  border: 1px solid #6c2535;
  color: #ffb4c0;
  border-radius: 10px;
  padding: 1rem 1.2rem;
}

.numeric-note {
  margin-top: 0.8rem;
  font-size: 0.9rem;
  color: var(--muted);
}

footer {
  text-align: center;
  color: var(--muted);
  font-size: 0.8rem;
  padding: 1.5rem 1rem 2.5rem;
}

@media (max-width: 480px) {
  .bounds { grid-template-columns: 1fr; }
  header h1 { font-size: 1.9rem; }
}