:root {
  --bg: #f4f6fb;
  --bg-grad-1: #0b1f3a;
  --bg-grad-2: #14305f;
  --card: #ffffff;
  --card-2: #fbfcfe;
  --card-3: #fafbfe;
  --ink: #0f1b2d;
  --ink-2: #52617a;
  --ink-3: #8a94a8;
  --ink-4: #98a2b6;
  --line: #e6eaf2;
  --seg-bg: #f1f4fa;
  --accent: #2f6bff;
  --accent-2: #18b7a8;
  --accent-soft: #eaf1ff;
  --ok: #16a34a;
  --warn: #d97706;
  --err: #dc2626;
  --err-soft: #fef2f2;
  --err-line: #fecaca;
  --code-bg: #0f1b2d;
  --code-ink: #e8eefb;
  --code-c: #7db2ff;
  --canvas-bg: #ffffff;
  --nav-bg: rgba(11, 31, 58, 0.96);
  --nav-ink: #c9d6ee;
  --radius: 16px;
  --shadow: 0 6px 24px rgba(15, 27, 45, 0.07);
  --shadow-sm: 0 2px 8px rgba(15, 27, 45, 0.06);
}

/* ---------- 深色模式 ---------- */
html[data-theme="dark"] {
  --bg: #0b111c;
  --bg-grad-1: #0a1c36;
  --bg-grad-2: #123158;
  --card: #151d2b;
  --card-2: #1a2334;
  --card-3: #182131;
  --ink: #e7edf7;
  --ink-2: #a3b0c4;
  --ink-3: #7e8ba3;
  --ink-4: #6b7890;
  --line: #2b3548;
  --seg-bg: #1a2334;
  --accent: #4d82ff;
  --accent-2: #25c4b4;
  --accent-soft: #1c2c4a;
  --err: #ff6b6b;
  --err-soft: #2a1a1a;
  --err-line: #5c2a2a;
  --code-bg: #0a1220;
  --code-ink: #dbe6f5;
  --code-c: #7db2ff;
  --canvas-bg: #151d2b;
  --nav-bg: rgba(8, 18, 34, 0.96);
  --nav-ink: #c9d6ee;
  --shadow: 0 6px 24px rgba(0, 0, 0, 0.45);
  --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.4);
}

html[data-theme="dark"] select,
html[data-theme="dark"] select option {
  background: #1a2334;
  color: #e7edf7;
}

html[data-theme="dark"] ::-webkit-scrollbar-thumb { background: #3a4658; }
html[data-theme="dark"] ::-webkit-scrollbar-thumb:hover { background: #4a5870; }

* { box-sizing: border-box; margin: 0; padding: 0; }

html { scroll-behavior: smooth; }

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "Helvetica Neue", Arial, sans-serif;
  background: var(--bg);
  color: var(--ink);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
  transition: background 0.25s, color 0.25s;
}

/* ---------- 顶部导航 ---------- */
.topnav {
  display: flex; align-items: center; flex-wrap: wrap; gap: 6px; padding: 10px 18px;
  background: var(--nav-bg); border-bottom: 1px solid rgba(255,255,255,0.08);
}
.topnav a {
  color: var(--nav-ink); text-decoration: none; font-size: 14px; font-weight: 500;
  padding: 7px 14px; border-radius: 999px; transition: all .15s; white-space: nowrap;
}
.topnav a:hover { color: #fff; background: rgba(255,255,255,0.1); }
.topnav a.active { color: #fff; background: var(--accent); }
.topnav .spacer { flex: 1; }
.theme-btn {
  border: 1px solid rgba(255,255,255,0.22); background: rgba(255,255,255,0.08); color: var(--nav-ink);
  padding: 7px 14px; border-radius: 999px; font-size: 13px; font-weight: 500; cursor: pointer;
  font-family: inherit; transition: all .15s; white-space: nowrap;
}
.theme-btn:hover { background: rgba(255,255,255,0.16); color: #fff; }

/* ---------- 顶部 ---------- */
.hero {
  background: linear-gradient(135deg, var(--bg-grad-1) 0%, var(--bg-grad-2) 55%, #1a4a8a 100%);
  color: #fff;
  padding: 44px 24px 52px;
  position: relative;
  overflow: hidden;
}
.hero::after {
  content: "";
  position: absolute;
  right: -120px; top: -120px;
  width: 380px; height: 380px;
  background: radial-gradient(circle, rgba(47, 107, 255, 0.35), transparent 65%);
  border-radius: 50%;
}
.hero::before {
  content: "";
  position: absolute;
  left: 18%; bottom: -180px;
  width: 420px; height: 420px;
  background: radial-gradient(circle, rgba(24, 183, 168, 0.25), transparent 60%);
  border-radius: 50%;
}
.hero-inner { max-width: 1120px; margin: 0 auto; position: relative; z-index: 1; }
.hero .tag {
  display: inline-block;
  font-size: 12px;
  letter-spacing: 1px;
  padding: 5px 12px;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.12);
  border: 1px solid rgba(255, 255, 255, 0.22);
  margin-bottom: 16px;
}
.hero h1 { font-size: 34px; font-weight: 700; letter-spacing: 0.5px; margin-bottom: 10px; }
.hero h1 .accent { color: #7db2ff; }
.hero p.sub { font-size: 15px; color: rgba(255, 255, 255, 0.82); max-width: 640px; }

/* ---------- 主体布局 ---------- */
.wrap { max-width: 1120px; margin: -26px auto 0; padding: 0 20px 60px; position: relative; z-index: 2; }

.layout { display: grid; grid-template-columns: 380px 1fr; gap: 22px; align-items: start; }
@media (max-width: 900px) { .layout { grid-template-columns: 1fr; } }

.card {
  background: var(--card);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  border: 1px solid var(--line);
  transition: background 0.25s, border-color 0.25s;
}

/* ---------- 计算面板 ---------- */
.panel { padding: 22px; }
.panel h2 {
  font-size: 13px; font-weight: 600; text-transform: uppercase; letter-spacing: 1px;
  color: var(--ink-2); margin-bottom: 16px; display: flex; align-items: center; gap: 8px;
}
.panel h2::before { content: ""; width: 4px; height: 16px; background: var(--accent); border-radius: 2px; }

.field { margin-bottom: 16px; }
.field label { display: block; font-size: 13px; font-weight: 600; color: var(--ink-2); margin-bottom: 7px; }
.field .hint { font-size: 12px; color: var(--ink-3); font-weight: 400; margin-left: 4px; }

/* 流体选择 chips */
.chips { display: flex; flex-wrap: wrap; gap: 8px; }
.chip {
  border: 1px solid var(--line); background: var(--card); color: var(--ink);
  padding: 8px 13px; border-radius: 10px; font-size: 13px; cursor: pointer;
  transition: all 0.15s ease; user-select: none;
}
.chip:hover { border-color: var(--accent); color: var(--accent); }
.chip.active { background: var(--accent); border-color: var(--accent); color: #fff; box-shadow: 0 4px 12px rgba(47, 107, 255, 0.3); }

/* 流体下拉 */
.fluid-select {
  width: 100%; height: 44px; border: 1px solid var(--line); border-radius: 10px;
  padding: 0 12px; font-size: 14px; color: var(--ink); background: var(--card-2);
  cursor: pointer; outline: none; font-family: inherit;
  transition: border-color 0.15s, box-shadow 0.15s;
}
.fluid-select:focus { border-color: var(--accent); box-shadow: 0 0 0 3px rgba(47, 107, 255, 0.12); background: var(--card); }
.fluid-select optgroup { font-weight: 600; color: var(--ink-2); font-style: normal; }
.fluid-select option { color: var(--ink); font-weight: 400; padding: 4px 0; }

/* 无输运性质的灰色卡片 */
.prop.dim { opacity: 0.55; }
.prop.dim .v { color: var(--ink-3); }

/* 输入模式 segmented */
.seg { display: flex; background: var(--seg-bg); border-radius: 10px; padding: 3px; gap: 3px; }
.seg button {
  flex: 1; border: none; background: transparent; padding: 8px 6px; border-radius: 8px;
  font-size: 13px; font-weight: 500; color: var(--ink-2); cursor: pointer; transition: all 0.15s;
}
.seg button.active { background: var(--card); color: var(--ink); box-shadow: var(--shadow-sm); font-weight: 600; }

/* 输入框 */
.input-row { display: flex; gap: 8px; align-items: center; }
.input-box {
  flex: 1; display: flex; align-items: center; border: 1px solid var(--line); border-radius: 10px;
  padding: 0 12px; height: 44px; background: var(--card-2); transition: border-color 0.15s, box-shadow 0.15s;
}
.input-box:focus-within { border-color: var(--accent); box-shadow: 0 0 0 3px rgba(47, 107, 255, 0.12); background: var(--card); }
.input-box input {
  flex: 1; border: none; outline: none; background: transparent; font-size: 15px; font-weight: 600;
  color: var(--ink); font-family: inherit; min-width: 0;
}
.input-box .unit { font-size: 12px; color: var(--ink-2); white-space: nowrap; }
.unit-select { border: 1px solid var(--line); border-radius: 10px; height: 44px; padding: 0 10px; font-size: 13px; color: var(--ink); background: var(--card); cursor: pointer; outline: none; }

/* 错误提示 */
.error-box {
  margin-top: 14px; background: var(--err-soft); border: 1px solid var(--err-line); color: var(--err);
  border-radius: 10px; padding: 10px 14px; font-size: 13px; display: none;
}
.error-box.show { display: block; }

.range-hint { margin-top: 12px; font-size: 12px; color: var(--ink-3); line-height: 1.5; }

/* ---------- 结果面板 ---------- */
.results { padding: 22px; min-height: 480px; }
.results h2 { font-size: 13px; font-weight: 600; text-transform: uppercase; letter-spacing: 1px; color: var(--ink-2); margin-bottom: 6px; }
.results .state-line { font-size: 13px; color: var(--ink-2); margin-bottom: 18px; }
.results .state-line b { color: var(--ink); }

.state-badge { display: inline-block; padding: 3px 10px; border-radius: 999px; font-size: 12px; font-weight: 600; background: var(--accent-soft); color: var(--accent); margin-right: 8px; }

.fluid-name { display: inline-block; font-size: 13px; font-weight: 700; color: var(--ink); margin-right: 10px; }

/* 物性网格 */
.props-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 12px; }
@media (max-width: 640px) { .props-grid { grid-template-columns: repeat(2, 1fr); } }
.prop {
  background: var(--card-3); border: 1px solid var(--line); border-radius: 12px; padding: 13px 15px;
  transition: transform 0.12s;
}
.prop:hover { transform: translateY(-2px); box-shadow: var(--shadow-sm); }
.prop .k { font-size: 12px; color: var(--ink-2); margin-bottom: 4px; }
.prop .v { font-size: 19px; font-weight: 700; color: var(--ink); font-variant-numeric: tabular-nums; }
.prop .u { font-size: 11px; color: var(--ink-3); margin-left: 3px; font-weight: 500; }

/* 饱和态双列 */
.sat-cols { display: grid; grid-template-columns: 1fr 1fr; gap: 14px; }
.sat-col { border: 1px solid var(--line); border-radius: 12px; padding: 14px; }
.sat-col h3 { font-size: 13px; font-weight: 700; margin-bottom: 10px; padding-bottom: 8px; border-bottom: 1px solid var(--line); }
.sat-col.liquid h3 { color: var(--accent); }
.sat-col.vapor h3 { color: var(--accent-2); }
.sat-row { display: flex; justify-content: space-between; font-size: 13px; padding: 5px 0; }
.sat-row .k { color: var(--ink-2); }
.sat-row .v { font-weight: 600; font-variant-numeric: tabular-nums; }
.hfg-note { margin-top: 14px; background: var(--accent-soft); border-radius: 10px; padding: 10px 14px; font-size: 13px; color: var(--accent); }

/* 空状态 */
.empty { text-align: center; color: var(--ink-3); padding: 80px 20px; }
.empty .ico { font-size: 44px; margin-bottom: 12px; opacity: 0.5; }

/* ---------- 方法论区块 ---------- */
.method { margin-top: 26px; padding: 26px; }
.method h2 { font-size: 16px; font-weight: 700; margin-bottom: 6px; }
.method .sub { font-size: 13px; color: var(--ink-2); margin-bottom: 22px; }

/* 抽屉式收纳 */
.method-toggle {
  display: flex; align-items: center; justify-content: space-between; width: 100%;
  background: transparent; border: none; cursor: pointer; padding: 0;
  font-family: inherit; text-align: left; color: var(--ink);
}
.method-toggle h2 { margin: 0; }
.method-toggle .chevron {
  width: 10px; height: 10px; flex: none; position: relative; display: inline-block;
  margin-left: 8px;
}
.method-toggle .chevron::before {
  content: ""; position: absolute; left: 1px; top: 0;
  width: 6px; height: 6px;
  border-left: 2px solid var(--ink-2);
  border-bottom: 2px solid var(--ink-2);
  transform: rotate(-45deg);
  transition: transform 0.25s;
}
.method.open .chevron::before { transform: rotate(135deg); }
.method-body { max-height: 0; overflow: hidden; transition: max-height 0.35s ease; }
.method.open .method-body { max-height: 6000px; }
.method-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(300px, 1fr)); gap: 18px; }
.m-card { border: 1px solid var(--line); border-radius: 12px; padding: 18px; background: var(--card-2); }
.m-card h3 { font-size: 14px; font-weight: 700; margin-bottom: 10px; display: flex; align-items: center; gap: 8px; }
.m-card h3 .n { width: 22px; height: 22px; border-radius: 6px; background: var(--accent); color: #fff; font-size: 12px; display: flex; align-items: center; justify-content: center; }
.m-card p { font-size: 13px; color: var(--ink-2); margin-bottom: 10px; }
.m-card .eq {
  background: var(--code-bg); color: var(--code-ink); border-radius: 8px; padding: 10px 14px;
  font-family: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
  font-size: 12.5px; overflow-x: auto; white-space: pre; line-height: 1.7;
}
.m-card .eq .c { color: var(--code-c); }

.footer { max-width: 1120px; margin: 30px auto 40px; padding: 0 20px; font-size: 12px; color: var(--ink-4); text-align: center; }
.footer a { color: var(--accent); text-decoration: none; }

/* 压焓图 */
.ph-diagram { grid-column: 1 / -1; }
.ph-diagram h2 { font-size: 16px; font-weight: 700; margin-bottom: 6px; }
.ph-diagram .sub { font-size: 13px; color: var(--ink-2); margin-bottom: 18px; }
.ph-toolbar { margin-bottom: 10px; }
.ph-reset {
  border: 1px solid var(--line); background: var(--card); color: var(--ink-2);
  padding: 6px 14px; border-radius: 8px; font-size: 13px; cursor: pointer;
  font-family: inherit; transition: all .15s;
}
.ph-reset:hover { border-color: var(--accent); color: var(--accent); }
.ph-diagram canvas { width: 100%; height: auto; display: block; border: 1px solid var(--line); border-radius: 10px; background: var(--canvas-bg); touch-action: none; }

::-webkit-scrollbar { width: 10px; height: 10px; }
::-webkit-scrollbar-thumb { background: #cdd4e0; border-radius: 6px; }
::-webkit-scrollbar-thumb:hover { background: #b3bccb; }

/* ---------- 响应式（移动端） ---------- */
@media (max-width: 640px) {
  .topnav { padding: 8px 12px; gap: 4px; }
  .topnav a { font-size: 13px; padding: 6px 11px; }
  .theme-btn { font-size: 12px; padding: 6px 11px; }

  .hero { padding: 30px 18px 40px; }
  .hero h1 { font-size: 25px; }
  .hero p.sub { font-size: 13px; }

  .wrap { padding: 0 12px 40px; margin-top: -18px; }
  .panel, .results { padding: 16px; }
  .results { min-height: 0; }

  .props-grid { grid-template-columns: repeat(2, 1fr); gap: 8px; }
  .prop { padding: 10px 12px; }
  .prop .v { font-size: 16px; }

  .sat-cols { grid-template-columns: 1fr; }
  .method { padding: 18px; }
  .ph-diagram { padding: 16px; }
}