:root {
  --bg: #f6f5f1;
  --surface: #ffffff;
  --surface-2: #eeede7;
  --ink: #24231f;
  --ink-2: #56544c;
  --muted: #6b685d;
  --line: #e7e5dc;
  --line-strong: #d9d6ca;
  --accent: #5f7c61;
  --accent-deep: #42584a;
  --accent-soft: #e6ece1;
  --ok: #4f9d6b;
  --danger: #b0594b;
  --shadow-sm: 0 1px 2px rgba(36, 35, 31, 0.05), 0 4px 12px rgba(36, 35, 31, 0.05);
  --font-display: 'Space Grotesk', 'PingFang SC', 'Microsoft YaHei', system-ui, sans-serif;
  --font-body: 'Inter', 'PingFang SC', 'Microsoft YaHei', system-ui, sans-serif;
  --font-mono: 'IBM Plex Mono', 'SFMono-Regular', Consolas, monospace;
}

* { box-sizing: border-box; }

:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
  border-radius: 6px;
}

a { color: inherit; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: var(--font-body);
  -webkit-font-smoothing: antialiased;
}

.shell {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

.topbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 20px;
  padding: 18px clamp(20px, 5vw, 72px);
  border-bottom: 1px solid var(--line);
  background: color-mix(in srgb, var(--bg) 82%, transparent);
  backdrop-filter: blur(8px);
  position: sticky;
  top: 0;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 12px;
  text-decoration: none;
}

.brand__mark {
  width: 36px;
  height: 36px;
  display: grid;
  place-items: center;
  border-radius: 10px;
  box-shadow: var(--shadow-sm);
}

.brand__mark svg { width: 36px; height: 36px; display: block; }

.brand__word {
  display: flex;
  flex-direction: column;
  line-height: 1.15;
}

.brand__word strong {
  font-family: var(--font-display);
  font-size: 16px;
  font-weight: 700;
}

.brand__word small {
  display: block;
  margin-top: 4px;
  font-family: var(--font-mono);
  font-size: 9px;
  letter-spacing: 0.22em;
  color: var(--muted);
}

.topbar__meta {
  display: flex;
  align-items: center;
  gap: 22px;
}

.back { font-size: 13px; color: var(--muted); text-decoration: none; }
.back:hover { color: var(--accent-deep); }

.status {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  font-size: 13px;
  color: var(--ink-2);
}

.status__dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--ok);
  box-shadow: 0 0 0 4px rgba(79, 157, 107, 0.14);
}

.main {
  flex: 1;
  width: min(1120px, calc(100% - 40px));
  margin: 0 auto;
  padding: 40px 0 60px;
}

.hero {
  max-width: 760px;
  margin-bottom: 24px;
}

.eyebrow {
  display: flex;
  align-items: center;
  gap: 12px;
  margin: 0 0 16px;
  font-family: var(--font-mono);
  font-size: 12px;
  letter-spacing: 0.16em;
  color: var(--muted);
  text-transform: uppercase;
}

.eyebrow__rule {
  width: 34px;
  height: 2px;
  border-radius: 2px;
  background: var(--accent);
}

.hero__title {
  margin: 0 0 14px;
  font-family: var(--font-display);
  font-size: clamp(25px, 5vw, 40px);
  font-weight: 700;
  letter-spacing: 0;
  line-height: 1.05;
}

.hero__lead {
  margin: 0;
  font-size: 16px;
  line-height: 1.7;
  color: var(--ink-2);
  max-width: 640px;
}

.workspace {
  display: grid;
  grid-template-columns: 300px minmax(0, 1fr);
  gap: 22px;
  align-items: start;
}

@media (max-width: 920px) {
  .workspace { grid-template-columns: 1fr; }
}

.panel {
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 18px;
  box-shadow: var(--shadow-sm);
  overflow: hidden;
}

.panel__title {
  margin: 0;
  padding: 14px 20px;
  font-size: 12px;
  font-weight: 600;
  letter-spacing: 0.08em;
  color: var(--ink-2);
  text-transform: uppercase;
  background: var(--surface-2);
  border-bottom: 1px solid var(--line);
}

.panel__body { padding: 20px; }

.field { display: block; margin-bottom: 16px; }
.field__label { display: block; font-size: 13px; color: var(--ink); margin-bottom: 6px; }

.field__control {
  display: flex;
  align-items: center;
  border: 1px solid var(--line-strong);
  border-radius: 10px;
  background: var(--surface);
}

.field__control:focus-within {
  border-color: var(--accent);
  box-shadow: 0 0 0 4px rgba(95, 124, 97, 0.14);
}

.field__control input {
  flex: 1;
  min-width: 0;
  border: none;
  background: none;
  padding: 11px 14px;
  font-family: var(--font-mono);
  font-size: 15px;
  color: var(--ink);
  outline: none;
}

.hint {
  font-size: 12px;
  line-height: 1.7;
  color: var(--muted);
  border-left: 3px solid var(--line-strong);
  padding-left: 10px;
  margin: 12px 0 0;
}

.footer {
  padding: 16px 28px;
  border-top: 1px solid var(--line);
  color: var(--muted);
  font-family: var(--font-mono);
  font-size: 10px;
  letter-spacing: 0.08em;
}

/* ---- plot / controls ---- */
.select {
  width: 100%;
  border: 1px solid var(--line-strong);
  border-radius: 10px;
  background: var(--surface);
  padding: 10px 12px;
  font-family: var(--font-body);
  font-size: 14px;
  color: var(--ink);
  outline: none;
}
.select:focus { border-color: var(--accent); }

.fn-list { display: flex; flex-direction: column; gap: 10px; margin-bottom: 14px; }
.fn-list:empty { margin-bottom: 0; }

.fn-row {
  border: 1px solid var(--line);
  border-radius: 12px;
  background: var(--surface);
  padding: 10px 12px;
}

.fn-row .fn-head {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 8px;
}

.fn-color {
  width: 20px;
  height: 20px;
  border-radius: 6px;
  border: none;
  cursor: pointer;
  flex: none;
  position: relative;
}
.fn-color::after {
  content: '';
  position: absolute;
  inset: -3px;
  border: 1px solid transparent;
  border-radius: 8px;
}
.fn-color:focus-visible::after { border-color: var(--accent); }

.fn-name {
  flex: 1;
  font-family: var(--font-mono);
  font-size: 12px;
  color: var(--muted);
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.fn-vis {
  border: none;
  background: none;
  cursor: pointer;
  font-size: 16px;
  line-height: 1;
  color: var(--muted);
  padding: 2px 4px;
}
.fn-vis:hover { color: var(--ink); }

.fn-del {
  border: none;
  background: none;
  cursor: pointer;
  font-size: 14px;
  line-height: 1;
  color: var(--muted);
  padding: 2px 4px;
}
.fn-del:hover { color: var(--danger); }

.fn-row .fn-expr {
  width: 100%;
  border: 1px solid var(--line-strong);
  border-radius: 8px;
  background: var(--surface);
  padding: 8px 10px;
  font-family: var(--font-mono);
  font-size: 14px;
  color: var(--ink);
  outline: none;
  margin-bottom: 6px;
}
.fn-row .fn-expr:focus { border-color: var(--accent); }
.fn-expr.fn-expr--err { border-color: var(--danger); }

.fn-preview {
  min-height: 20px;
  font-size: 13px;
  color: var(--ink-2);
  overflow-x: auto;
  white-space: nowrap;
}
.fn-preview .katex { font-size: 1.05em; }
.fn-preview.fn-preview--err { color: var(--danger); }

.btn {
  border: 1px solid var(--line-strong);
  border-radius: 10px;
  background: var(--surface);
  color: var(--ink);
  padding: 9px 14px;
  font-size: 13px;
  font-weight: 600;
  cursor: pointer;
  transition: background 0.16s, border-color 0.16s;
}
.btn:hover { background: var(--surface-2); }
.btn--ghost { width: 100%; border-style: dashed; }

.toggle {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 7px 0;
  cursor: pointer;
  user-select: none;
}
.toggle input { position: absolute; opacity: 0; pointer-events: none; }
.toggle__track {
  width: 38px;
  height: 22px;
  flex: none;
  border-radius: 999px;
  background: var(--line-strong);
  position: relative;
  transition: background 0.18s;
}
.toggle__track::after {
  content: '';
  position: absolute;
  top: 2px;
  left: 2px;
  width: 18px;
  height: 18px;
  border-radius: 50%;
  background: #fff;
  box-shadow: 0 1px 2px rgba(0,0,0,0.2);
  transition: transform 0.18s;
}
.toggle input:checked + .toggle__track { background: var(--accent); }
.toggle input:checked + .toggle__track::after { transform: translateX(16px); }
.toggle input:focus-visible + .toggle__track { outline: 2px solid var(--accent); outline-offset: 2px; }
.toggle__label { font-size: 13px; color: var(--ink); }

.inline-field {
  display: flex;
  align-items: center;
  gap: 8px;
  margin: 6px 0 14px;
}
.inline-field .field__label { margin: 0; flex: none; font-size: 12px; }
.inline-field .field__control { flex: 1; min-width: 0; }
.inline-field input {
  width: 100%;
  border: none;
  background: none;
  padding: 8px 10px;
  font-family: var(--font-mono);
  font-size: 13px;
  color: var(--ink);
  outline: none;
}

/* ---- plot ---- */
.plot__body { padding: 14px; }
.plot__wrap {
  position: relative;
  width: 100%;
  border: 1px solid var(--line);
  border-radius: 12px;
  overflow: hidden;
  background: var(--surface);
}
#plot { display: block; width: 100%; height: 520px; touch-action: none; }
.plot__empty {
  position: absolute;
  inset: 0;
  display: grid;
  place-items: center;
  color: var(--muted);
  font-size: 14px;
  pointer-events: none;
}
.plot__tip {
  margin: 12px 2px 0;
  font-size: 12px;
  color: var(--muted);
}
@media (max-width: 720px) {
  #plot { height: 380px; }
}

/* ---- view tabs / 3D / complex ---- */
.view-tabs {
  display: inline-flex;
  gap: 4px;
  padding: 4px;
  background: var(--surface-2);
  border-radius: 12px;
  margin-bottom: 14px;
}
.view-tab {
  border: none;
  background: none;
  padding: 8px 16px;
  border-radius: 9px;
  font-family: var(--font-body);
  font-size: 13px;
  font-weight: 600;
  color: var(--ink-2);
  cursor: pointer;
  transition: background 0.16s, color 0.16s;
}
.view-tab:hover { color: var(--accent-deep); }
.view-tab.is-active {
  background: var(--surface);
  color: var(--accent-deep);
  box-shadow: var(--shadow-sm);
}

.view-input {
  display: flex;
  align-items: center;
  gap: 12px;
  margin-bottom: 14px;
}
.view-input__label {
  flex: none;
  font-size: 13px;
  color: var(--ink);
  font-family: var(--font-mono);
}
.view-input__control {
  flex: 1;
  display: flex;
  border: 1px solid var(--line-strong);
  border-radius: 10px;
  background: var(--surface);
}
.view-input__control:focus-within {
  border-color: var(--accent);
  box-shadow: 0 0 0 4px rgba(95, 124, 97, 0.14);
}
.view-input input {
  flex: 1;
  min-width: 0;
  border: none;
  background: none;
  padding: 10px 13px;
  font-family: var(--font-mono);
  font-size: 14px;
  color: var(--ink);
  outline: none;
}

.workspace--wide { grid-template-columns: 1fr; }

#plot3d, #plotComplex {
  display: block;
  width: 100%;
  height: 520px;
}
@media (max-width: 720px) {
  #plot3d, #plotComplex { height: 380px; }
}
.view-input[hidden] { display: none; }
.plot__wrap[hidden] { display: none; }

/* ---- function type / param / polar / implicit ---- */
.fn-head { flex-wrap: wrap; }
.fn-type {
  border: 1px solid var(--line-strong);
  border-radius: 8px;
  background: var(--surface);
  padding: 5px 8px;
  font-family: var(--font-body);
  font-size: 12px;
  color: var(--ink);
  outline: none;
  cursor: pointer;
}
.fn-type:focus { border-color: var(--accent); }

.fn-inputs { display: flex; flex-direction: column; gap: 8px; }
.fn-inputs .fn-expr { margin-bottom: 0; }

.fn-range { display: flex; align-items: center; gap: 6px; }
.fn-range__label { flex: none; font-family: var(--font-mono); font-size: 11px; color: var(--muted); }
.fn-row .fn-range__input { width: 78px; padding: 6px 8px; }

/* ODE direction field canvas */
#plotOde { display: block; width: 100%; height: 520px; }
@media (max-width: 720px) { #plotOde { height: 380px; } }

.plot-actions {
  display: flex;
  justify-content: flex-end;
  margin: 0 2px 10px;
}

/* ---- function palette ---- */
.fn-pal { display: flex; flex-wrap: wrap; gap: 6px; margin-top: 12px; }
.fn-pal button {
  border: 1px solid var(--line-strong);
  background: var(--surface);
  color: var(--ink-2);
  border-radius: 7px;
  padding: 5px 9px;
  font-family: var(--font-mono);
  font-size: 12px;
  cursor: pointer;
  transition: background .15s, border-color .15s, color .15s;
}
.fn-pal button:hover { background: var(--accent-soft); border-color: var(--accent); color: var(--accent-deep); }
.fn-pal__hint { font-size: 11px; color: var(--muted); margin: 8px 0 0; }

/* ---- 3D controls ---- */
.p3d-controls[hidden] { display: none !important; }
.p3d-controls { display: flex; flex-wrap: wrap; gap: 10px; align-items: center; margin-bottom: 14px; padding: 10px 12px; background: var(--surface-2); border: 1px solid var(--line); border-radius: 10px; }
.p3d-controls label { display: inline-flex; align-items: center; gap: 6px; font-size: 12px; color: var(--ink-2); white-space: nowrap; }
.p3d-controls input, .p3d-controls select { border: 1px solid var(--line-strong); border-radius: 7px; background: var(--surface); color: var(--ink); padding: 5px 7px; font-family: var(--font-mono); font-size: 12px; outline: none; }
.p3d-controls input { width: 56px; }
.p3d-controls input:focus, .p3d-controls select:focus { border-color: var(--accent); }

/* ===== 控件美化（按钮/输入框/下拉框），跟随绿/紫主题 ===== */
/* 按钮 */
.btn {
  background: linear-gradient(135deg, var(--surface) 0%, var(--surface-2) 100%);
  box-shadow: var(--shadow-sm);
  font-family: var(--font-body);
  letter-spacing: 0.01em;
  transition: background 0.18s, border-color 0.18s, color 0.18s, transform 0.18s, box-shadow 0.18s;
}
.btn:hover {
  background: var(--accent-soft);
  border-color: var(--accent);
  color: var(--accent-deep);
  transform: translateY(-1px);
  box-shadow: 0 4px 14px color-mix(in srgb, var(--accent) 22%, transparent);
}
.btn:active { transform: translateY(0); box-shadow: none; }
.btn:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
.btn--primary { background: var(--accent); border-color: var(--accent); color: #fff; }
.btn--primary:hover { background: var(--accent-deep); border-color: var(--accent-deep); color: #fff; transform: translateY(-1px); }

/* 输入框：统一圆角 + 内阴影 + 聚焦光环 */
.fn-expr, .view-input__control, .field__control input, .p3d-controls input, .p3d-controls select {
  border-radius: 9px;
  background: var(--surface);
  box-shadow: inset 0 1px 2px rgba(36, 35, 31, 0.03);
  transition: border-color 0.16s, box-shadow 0.16s;
}
.fn-expr:hover, .view-input__control:hover, .select:hover, .fn-type:hover {
  border-color: color-mix(in srgb, var(--accent) 42%, var(--line-strong));
}
.fn-expr:focus, .view-input__control:focus-within, .p3d-controls input:focus, .p3d-controls select:focus {
  border-color: var(--accent) !important;
  box-shadow: 0 0 0 3px color-mix(in srgb, var(--accent) 16%, transparent) !important;
}
.fn-expr.fn-expr--err { border-color: var(--danger) !important; box-shadow: 0 0 0 3px color-mix(in srgb, var(--danger) 14%, transparent) !important; }

/* 下拉框：去掉原生箭头，自定义主题箭头 */
.fn-type, .select, .p3d-controls select {
  -webkit-appearance: none; -moz-appearance: none; appearance: none;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='10' height='6' viewBox='0 0 10 6'%3E%3Cpath d='M1 1l4 4 4-4' fill='none' stroke='%236b685d' stroke-width='1.6' stroke-linecap='round' stroke-linejoin='round'/%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: right 12px center;
  padding-right: 30px;
  cursor: pointer;
  transition: border-color 0.16s, box-shadow 0.16s, background-color 0.16s;
}
.fn-type:hover, .select:hover, .p3d-controls select:hover { background-color: var(--accent-soft); }

/* 函数类型下拉 / 基准下拉 */
.fn-type, .select { font-weight: 500; }

/* 微积分 tabs */
.view-tab {
  transition: color 0.16s, background 0.16s, border-color 0.16s;
  font-weight: 500;
}
.view-tab:hover { color: var(--accent-deep); background: var(--accent-soft); border-color: var(--accent); }
.view-tab.is-active {
  background: linear-gradient(135deg, var(--accent) 0%, var(--accent-deep) 100%);
  border-color: var(--accent-deep);
  color: #fff;
  box-shadow: 0 3px 10px color-mix(in srgb, var(--accent) 26%, transparent);
}

/* 函数面板 chips */
.fn-pal button {
  background: linear-gradient(135deg, var(--surface) 0%, var(--surface-2) 100%);
  box-shadow: var(--shadow-sm);
  border-radius: 8px;
  transition: background 0.16s, border-color 0.16s, color 0.16s, transform 0.16s, box-shadow 0.16s;
}
.fn-pal button:hover { background: var(--accent-soft); border-color: var(--accent); color: var(--accent-deep); transform: translateY(-1px); box-shadow: 0 3px 8px color-mix(in srgb, var(--accent) 20%, transparent); }

/* p3d 控制面板 */
.p3d-controls { box-shadow: var(--shadow-sm); }