/* 极简计算器 · 原创样式（无外链字体、无 CDN、无第三方 CSS） */
:root {
  --bg: #f5f6f8;
  --panel: #ffffff;
  --key: #ffffff;
  --key-fg: #16181d;
  --fn-bg: #e7e9ee;
  --op-bg: #1f2937;
  --op-fg: #ffffff;
  --eq-bg: #2f6bff;
  --fg: #16181d;
  --fg-dim: #6b7280;
  --border: rgba(0, 0, 0, .08);
  --accent: #2f6bff;
  --shadow: 0 1px 2px rgba(16, 24, 40, .06), 0 8px 24px rgba(16, 24, 40, .06);
  --radius: 16px;
  --gap: 10px;
  --display-size: 44px;
}

html[data-theme="dark"] {
  --bg: #0f1115;
  --panel: #171a21;
  --key: #1e222b;
  --key-fg: #e8eaf0;
  --fn-bg: #262b36;
  --op-bg: #2a303c;
  --op-fg: #e8eaf0;
  --eq-bg: #3d78ff;
  --fg: #e8eaf0;
  --fg-dim: #9aa3b2;
  --border: rgba(255, 255, 255, .09);
  --shadow: 0 1px 2px rgba(0, 0, 0, .4), 0 10px 30px rgba(0, 0, 0, .35);
}

@media (prefers-color-scheme: dark) {
  html[data-theme="auto"] {
    --bg: #0f1115;
    --panel: #171a21;
    --key: #1e222b;
    --key-fg: #e8eaf0;
    --fn-bg: #262b36;
    --op-bg: #2a303c;
    --op-fg: #e8eaf0;
    --eq-bg: #3d78ff;
    --fg: #e8eaf0;
    --fg-dim: #9aa3b2;
    --border: rgba(255, 255, 255, .09);
  }
}

* { box-sizing: border-box; -webkit-tap-highlight-color: transparent; }

html, body { height: 100%; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--fg);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Hiragino Sans GB",
               "Microsoft YaHei", "Noto Sans CJK SC", sans-serif;
  font-size: 16px;
  line-height: 1.4;
  -webkit-font-smoothing: antialiased;
  overscroll-behavior: none;
}

.app {
  max-width: 520px;
  margin: 0 auto;
  min-height: 100%;
  display: flex;
  flex-direction: column;
  padding: max(10px, env(safe-area-inset-top)) 14px calc(12px + env(safe-area-inset-bottom));
}

/* 顶栏 */
.topbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 4px 2px 10px;
}
.brand { display: flex; align-items: center; gap: 8px; }
.brand-mark {
  width: 28px; height: 28px; border-radius: 9px;
  background: var(--eq-bg); color: #fff;
  display: grid; place-items: center;
  font-weight: 700; font-size: 16px;
}
.brand-name { font-weight: 650; letter-spacing: .3px; }
.badge {
  font-size: 11px; font-weight: 700; letter-spacing: .5px;
  padding: 2px 6px; border-radius: 6px;
  background: var(--eq-bg); color: #fff;
}
.topbar-actions { display: flex; gap: 6px; }
.icon-btn {
  width: 36px; height: 36px; border-radius: 10px;
  border: 1px solid var(--border); background: var(--panel); color: var(--fg);
  display: grid; place-items: center; cursor: pointer; font-size: 15px;
}
.icon-btn svg { width: 19px; height: 19px; fill: none; stroke: currentColor; stroke-width: 1.7; stroke-linecap: round; }
.icon-btn:active { transform: scale(.94); }

/* 显示屏 */
.display {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 18px 18px 14px;
  margin-bottom: var(--gap);
  text-align: right;
  min-height: 128px;
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
}
.display-expr {
  color: var(--fg-dim);
  font-size: 15px;
  min-height: 22px;
  word-break: break-all;
  font-variant-numeric: tabular-nums;
}
.display-result {
  font-size: var(--display-size);
  font-weight: 620;
  letter-spacing: -1px;
  font-variant-numeric: tabular-nums;
  word-break: break-all;
  margin-top: 6px;
}
.display-result.is-error { color: #e5484d; font-size: 24px; }
.display-result.is-preview { color: var(--fg-dim); font-weight: 500; }
.display-hint { color: var(--fg-dim); font-size: 11.5px; margin-top: 8px; text-align: left; }

/* 科学键区 */
.sci {
  display: grid;
  grid-template-columns: repeat(8, 1fr);
  gap: 6px;
  margin-bottom: var(--gap);
}
.sci-btn {
  background: var(--fn-bg);
  color: var(--fg);
  border: 1px solid transparent;
  border-radius: 10px;
  padding: 9px 0;
  font-size: 13.5px;
  cursor: pointer;
}
.sci-btn:active { transform: scale(.93); }

/* 键盘 */
.keypad {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: var(--gap);
  flex: 1;
}
.key {
  background: var(--key);
  color: var(--key-fg);
  border: 1px solid var(--border);
  border-radius: 14px;
  min-height: 56px;
  font-size: 22px;
  font-weight: 520;
  cursor: pointer;
  box-shadow: var(--shadow);
}
.key:active { transform: scale(.96); background: var(--fn-bg); }
.key-fn { background: var(--fn-bg); font-size: 18px; }
.key-op { background: var(--op-bg); color: var(--op-fg); }
.key-op:active { background: var(--eq-bg); }
.key-eq { background: var(--eq-bg); color: #fff; font-size: 24px; }
.key-zero { grid-column: span 2; }

/* 底部 */
.foot {
  display: flex; align-items: center; justify-content: space-between;
  gap: 8px; padding: 12px 4px 0;
  font-size: 11.5px; color: var(--fg-dim);
  flex-wrap: wrap;
}
.link-btn {
  background: none; border: none; color: var(--accent);
  font-size: 12.5px; cursor: pointer; padding: 2px 0;
}
.link-btn.danger { color: #e5484d; }
.foot-note { opacity: .85; }

/* 抽屉 */
.sheet {
  position: fixed; inset: 0;
  background: rgba(8, 10, 14, .45);
  display: flex; align-items: flex-end; justify-content: center;
  z-index: 50;
}
.sheet[hidden] { display: none; }
.sheet-panel {
  background: var(--panel);
  width: 100%; max-width: 520px;
  border-radius: 20px 20px 0 0;
  padding: 18px 18px calc(20px + env(safe-area-inset-bottom));
  max-height: 88vh; overflow: auto;
  box-shadow: 0 -8px 40px rgba(0, 0, 0, .25);
}
.sheet-head {
  display: flex; align-items: center; justify-content: space-between;
  margin-bottom: 12px;
}
.sheet-head h2 { font-size: 17px; margin: 0; font-weight: 640; }
.sheet-head h2 small { color: var(--fg-dim); font-weight: 500; font-size: 13px; }
.sheet-head-actions { display: flex; align-items: center; gap: 10px; }
.sheet-foot {
  display: flex; align-items: center; justify-content: space-between;
  margin-top: 12px; padding-top: 10px; border-top: 1px solid var(--border);
}

/* 历史 */
.history-list { display: flex; flex-direction: column; gap: 8px; }
.history-item {
  background: var(--key); border: 1px solid var(--border);
  border-radius: 12px; padding: 10px 12px; cursor: pointer; text-align: right;
}
.history-item:active { background: var(--fn-bg); }
.history-item .h-expr { color: var(--fg-dim); font-size: 13px; word-break: break-all; }
.history-item .h-res { font-size: 19px; font-weight: 600; font-variant-numeric: tabular-nums; }
.history-empty { color: var(--fg-dim); text-align: center; padding: 26px 0; font-size: 13.5px; }

/* 设置行 */
.setting-row {
  display: flex; align-items: center; justify-content: space-between;
  padding: 12px 0; border-bottom: 1px solid var(--border); font-size: 14.5px;
}
.seg { display: flex; background: var(--fn-bg); border-radius: 9px; padding: 3px; }
.seg-btn {
  border: none; background: none; color: var(--fg-dim);
  font-size: 12.5px; padding: 6px 10px; border-radius: 7px; cursor: pointer;
}
.seg-btn.is-active { background: var(--panel); color: var(--fg); box-shadow: var(--shadow); font-weight: 600; }
.toggle {
  width: 46px; height: 27px; border-radius: 999px; border: none;
  background: var(--fn-bg); cursor: pointer; position: relative;
}
.toggle i {
  position: absolute; top: 3px; left: 3px; width: 21px; height: 21px;
  border-radius: 50%; background: #fff; box-shadow: 0 1px 3px rgba(0,0,0,.25);
  transition: transform .16s ease;
}
.toggle[aria-checked="true"] { background: var(--eq-bg); }
.toggle[aria-checked="true"] i { transform: translateX(19px); }
.about { color: var(--fg-dim); font-size: 12.5px; margin-top: 14px; }
.about p { margin: 6px 0; }

/* 订阅 */
.plan-list { display: flex; gap: 8px; }
.plan {
  flex: 1; background: var(--key); border: 1px solid var(--border);
  border-radius: 14px; padding: 12px 8px; text-align: center;
}
.plan-hot { border-color: var(--eq-bg); }
.plan-name { font-size: 12.5px; color: var(--fg-dim); }
.plan-name em { font-style: normal; color: var(--accent); font-size: 11px; }
.plan-price { font-size: 22px; font-weight: 650; margin: 4px 0 8px; }
.plan-price small { font-size: 11.5px; color: var(--fg-dim); font-weight: 400; }
.btn {
  width: 100%; padding: 9px 0; border-radius: 10px; border: 1px solid var(--border);
  background: var(--fn-bg); color: var(--fg); font-size: 13.5px; cursor: pointer;
}
.btn-primary { background: var(--eq-bg); border-color: var(--eq-bg); color: #fff; }
.pro-list { margin: 14px 0 8px; padding-left: 18px; color: var(--fg-dim); font-size: 13px; }
.pro-list li { margin: 4px 0; }
.pay-note { color: var(--fg-dim); font-size: 12px; margin: 6px 0; }
.pay-demo-note { opacity: .8; }

/* 单位换算 */
.unit-row { display: flex; align-items: center; gap: 6px; margin: 8px 0 12px; flex-wrap: wrap; }
.unit-row input, .unit-row select {
  flex: 1; min-width: 96px; padding: 10px; border-radius: 10px;
  border: 1px solid var(--border); background: var(--key); color: var(--fg); font-size: 15px;
}
.unit-eq { color: var(--fg-dim); }
.unit-result {
  font-size: 26px; font-weight: 620; text-align: right;
  font-variant-numeric: tabular-nums; padding: 8px 0;
}

/* 文档页（隐私政策等） */
.doc-page { background: var(--bg); color: var(--fg); }
.doc {
  max-width: 680px;
  margin: 0 auto;
  padding: 32px 20px 64px;
  line-height: 1.75;
  font-size: 15px;
}
.doc h1 { font-size: 24px; margin: 0 0 6px; }
.doc h2 { font-size: 17px; margin: 28px 0 10px; }
.doc ul { margin: 8px 0; padding-left: 20px; }
.doc li { margin: 6px 0; }
.doc-sub { color: var(--fg-dim); font-size: 13px; margin: 0 0 20px; }
.doc-foot { margin-top: 32px; }
.doc-foot a, .doc a { color: var(--accent); }

/* 开发对照块（生成器注入，上线前删除） */
.dev-pains {
  margin: 0 0 var(--gap);
  background: var(--panel);
  border: 1px dashed var(--border);
  border-radius: 12px;
  padding: 10px 14px;
  font-size: 13px;
}
.dev-pains summary { cursor: pointer; color: var(--fg-dim); }
.dev-pains .pains { margin: 10px 0 0; padding-left: 18px; }
.dev-pains .pains li { margin: 8px 0; }
.dev-pains .acceptance { margin: 4px 0 0; padding-left: 16px; color: var(--fg-dim); }

/* 提示条 */
.toast {
  position: fixed; left: 50%; bottom: 26px; transform: translateX(-50%);
  background: rgba(20, 22, 28, .93); color: #fff;
  padding: 10px 16px; border-radius: 999px; font-size: 13px;
  z-index: 90; max-width: 88vw; text-align: center;
}
.toast[hidden] { display: none; }

@media (max-width: 380px) {
  .sci { grid-template-columns: repeat(4, 1fr); }
  .key { min-height: 50px; font-size: 20px; }
  :root { --display-size: 36px; }
}