:root {
  --bg: #f3efe7;
  --card: #fffdf9;
  --ink: #1f2933;
  --muted: #52606d;
  --accent: #0b6e4f;
  --accent-press: #09553d;
  --danger: #b91c1c;
  --border: #d7ccc0;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: "Trebuchet MS", "Segoe UI", sans-serif;
  background: linear-gradient(180deg, #f7f1e8 0%, #efe7dc 100%);
  color: var(--ink);
  min-height: 100vh;
  display: flex;
  justify-content: center;
  padding: 16px;
}

.phone-shell {
  width: min(420px, 100%);
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 16px;
  padding: 18px;
  box-shadow: 0 10px 24px rgba(30, 41, 59, 0.1);
}

h1 {
  margin: 0;
  font-size: 1.65rem;
}

.subtitle {
  margin: 8px 0 18px;
  color: var(--muted);
  font-size: 0.95rem;
}

.solver-form {
  display: grid;
  gap: 10px;
}

.start-group {
  margin: 0;
  padding: 10px 12px;
  border-radius: 10px;
  border: 1px solid var(--border);
  display: grid;
  gap: 8px;
}

.start-group legend {
  padding: 0 4px;
  font-size: 0.95rem;
  font-weight: 600;
}

.choice {
  display: flex;
  gap: 8px;
  align-items: center;
  font-weight: 400;
}

label {
  font-size: 0.95rem;
  font-weight: 600;
}

input,
button {
  font: inherit;
}

input {
  padding: 10px 12px;
  border-radius: 10px;
  border: 1px solid var(--border);
  background: #fff;
}

.solver-form button {
  border: none;
  border-radius: 10px;
  padding: 11px 14px;
  background: var(--accent);
  color: #fff;
  font-weight: 700;
}

.solver-form button:active {
  background: var(--accent-press);
}

.error {
  color: var(--danger);
  margin: 12px 0 0;
}

.steps-panel {
  margin-top: 18px;
  border-top: 1px solid var(--border);
  padding-top: 14px;
}

.count,
.step-index {
  margin: 0;
  color: var(--muted);
  font-size: 0.95rem;
}

.step-box {
  margin-top: 10px;
  background: #f5f7f8;
  border-radius: 12px;
  border: 1px solid #d9e2ec;
  padding: 16px;
  text-align: center;
  font-size: 1.2rem;
  font-weight: 700;
  text-transform: capitalize;
  min-height: 64px;
  display: flex;
  align-items: center;
  justify-content: center;
}

.nav-row {
  margin-top: 12px;
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 10px;
}

.arrow {
  border: 1px solid var(--border);
  border-radius: 10px;
  background: #fff;
  padding: 12px;
  font-size: 1.3rem;
  font-weight: 700;
}

.arrow:disabled {
  opacity: 0.45;
}

@media (min-width: 768px) {
  body {
    padding: 36px;
  }

  .phone-shell {
    padding: 22px;
  }
}