:root {
  color-scheme: light;
  --bg: #f4f6fb;
  --panel: #ffffff;
  --ink: #1d2430;
  --muted: #5c677d;
  --line: #d6deeb;
  --accent: #0f5ad4;
  --error: #b42318;
}

*,
*::before,
*::after {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: "IBM Plex Sans", "Segoe UI", sans-serif;
  background: radial-gradient(circle at top left, #e6ecff, var(--bg) 45%);
  color: var(--ink);
}

#copyright { margin-top: 0.95rem; color: var(--muted); font-size: 0.95rem; display: flex; justify-content: center; text-align: center; }
#copyright p { margin: 0; }

.layout {
  max-width: 860px;
  margin: 0 auto;
  padding: 2rem 1rem 3rem;
}

header h1 {
  margin: 0 0 0.5rem;
  font-size: clamp(1.7rem, 2.5vw, 2.3rem);
}

header p {
  margin: 0 0 1.2rem;
  color: var(--muted);
}

.panel {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 1rem;
  margin-bottom: 1rem;
  box-shadow: 0 6px 22px rgba(17, 24, 39, 0.06);
}

form {
  display: grid;
  gap: 0.65rem;
}

.equation-hint {
  margin: 0;
  color: var(--muted);
  line-height: 1.45;
  font-size: 0.95rem;
}

.equation-hint code {
  background: #eef2f8;
  border: 1px solid #e0dfed;
  border-radius: 5px;
  margin: 0 0.08rem;
  padding: 0.04rem 0.26rem;
}

label {
  font-weight: 600;
}

textarea,
input {
  width: 100%;
  border: 1px solid #bdc9df;
  border-radius: 8px;
  padding: 0.65rem 0.75rem;
  font: inherit;
}

textarea:focus,
input:focus {
  outline: 2px solid #c5d6ff;
  border-color: var(--accent);
}

button {
  width: fit-content;
  border: none;
  border-radius: 8px;
  background: var(--accent);
  color: #fff;
  font: inherit;
  font-weight: 700;
  padding: 0.6rem 1rem;
  cursor: pointer;
}

button:hover {
  filter: brightness(1.07);
}

.result ul,
.result ol {
  margin-top: 0.5rem;
}

.error {
  color: var(--error);
  font-weight: 600;
}

.warning {
  color: #8b6300;
}