/* ========== Base / Reset ========== */
* {
    box-sizing: border-box;
}
html { 
    scroll-behavior: smooth; 
}
body {
    margin: 0;
    font-family: system-ui, -apple-system, Segoe UI, Roboto, "PingFang SC", "Noto Sans CJK SC", "Microsoft YaHei", Arial, sans-serif;
    line-height: 1.6;
    color: #0f172a; /* slate-900 */
    background: #f8fafc; /* slate-50 */
}

/* Theme tokens */
:root{
  --brand: #2563eb;        /* blue-600 */
  --brand-weak:#dbeafe;    /* blue-100 */
  --ink:#0f172a;
  --muted:#475569;         /* slate-600 */
  --card:#ffffff;
  --border:#e2e8f0;        /* slate-200 */
  --shadow: 0 8px 24px rgba(15,23,42,.08);
  --radius: 14px;
}

/* ========== Layout ========== */
header {
  background: var(--card);
  border-bottom: 1px solid var(--border);
  position: sticky; top: 0; z-index: 10;
  display: flex;
  justify-content: space-between;
  align-items: center;
}

header .wrap,
main .wrap,
footer .wrap {
  max-width: 960px;
  margin: 0 auto;
  padding: 16px 20px;
}

header h1{
  margin: 0;
  font-size: clamp(20px, 2.5vw, 28px);
  letter-spacing: .3px;
}
header p {
    margin: 6px 0 0; color: var(--muted);
    position: absolute;
    top: 70%;
}

/* ========== Nav ========== */
nav ul{
    list-style: none; margin: 10px 0 0; padding: 0; display: flex; gap: 16px;
}

nav > ul > li {
    position: relative;
}

nav a {
    display: inline-block;
    padding: 8px 10px;
    border-radius: 10px;
    text-decoration: none;
    color: var(--ink);
}

nav a:hover{
    background: var(--brand-weak); color: var(--brand);
}

/* dropdown (二级菜单) */
nav ul ul {
    position: absolute; left: 0; top: 100%;
    background: var(--card);
    border: 1px solid var(--border);
    border-radius: 12px;
    padding: 8px;
    display: none;
    box-shadow: var(--shadow);
    min-width: 220px;
}
nav ul li:hover > ul {
    display: block;
}
nav ul ul li a {
    width: 100%; padding: 8px 10px;
}

/* ========== Main Sections ========== */
main { padding: 18px 0 32px; }
section{
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 18px;
  margin: 18px 20px;
}
h2{
  margin: 0 0 14px;
  font-size: clamp(18px, 2.3vw, 22px);
}

/* Card grid（让多个工具排版更紧凑） */
@media (min-width: 760px){
  main .grid{
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 18px;
    margin: 0 20px;
  }
  main .grid section{ margin: 0; }
}

/* ========== Forms ========== */
label{
  display: block;
  font-size: 14px;
  color: var(--muted);
  margin: 10px 0 6px;
}
input[type="number"],
input[type="text"],
select{
  width: 100vh;
  padding: 10px 12px;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: #fff;
  outline: none;
  transition: border-color .15s ease, box-shadow .15s ease;
}
input:focus, select:focus{
  border-color: var(--brand);
  box-shadow: 0 0 0 3px rgba(37,99,235,.15);
}

.inline{
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
}
.inline-3{
  display: grid;
  grid-template-columns: repeat(3,1fr);
  gap: 12px;
}
.small-note{ color: var(--muted); font-size: 12px; }

/* Buttons */
button{
  appearance: none;
  border: 0;
  background: var(--brand);
  color: #fff;
  padding: 10px 14px;
  border-radius: 10px;
  margin-top: 12px;
  cursor: pointer;
  font-weight: 600;
  box-shadow: 0 6px 16px rgba(37,99,235,.25);
  transition: transform .06s ease, box-shadow .2s ease, opacity .2s ease;
}
button:hover{ opacity: .95; }
button:active{ transform: translateY(1px); box-shadow: 0 4px 12px rgba(37,99,235,.25); }

/* Results */
#lengthResult, #areaResult, #volumeResult, #bmiResult{
  margin-top: 10px;
  padding: 10px 12px;
  background: #f1f5f9; /* slate-100 */
  border: 1px solid var(--border);
  border-radius: 10px;
}

/* Temperature theme feedback */
.temp-warm { background: linear-gradient(180deg, #fff7ed, #ffffff); } /* amber-50 */
.temp-cold { background: linear-gradient(180deg, #eff6ff, #ffffff); } /* blue-50 */

/* ========== Footer ========== */
footer{
  border-top: 1px solid var(--border);
  background: var(--card);
}
footer .wrap{
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  padding: 18px 20px;
}
footer p{ margin: 0; color: var(--muted); }

/* ========== Responsive tweaks ========== */
@media (max-width: 640px){
  nav ul{ flex-wrap: wrap; }
  .inline, .inline-3{ grid-template-columns: 1fr; }
  section{ margin: 12px 12px; padding: 14px; }
  footer .wrap{ flex-direction: column; align-items: flex-start; }
}

/* ========== Dark mode (跟随系统) ========== */
@media (prefers-color-scheme: dark){
  :root{
    --ink:#e5e7eb;
    --muted:#94a3b8;
    --card:#0b1220;
    --border:#1f2a44;
    --brand-weak:#0b255e;
    --shadow: 0 8px 24px rgba(0,0,0,.45);
  }
  body{ background: #0a0f1a; color: var(--ink); }
  nav a{ color: var(--ink); }
  #lengthResult, #areaResult, #volumeResult, #bmiResult{
    background: #0f172a; border-color: #22304f;
  }
}

/* ========== Dark mode overrides (paste at end of styles.css) ========== */
body.dark-mode {
  background-color: #0b1116;    /* 页面整体深色背景 */
  color: #e6eef6;               /* 主文字 亮色 */
}

/* header / nav / footer 明确覆盖背景与文字 */
body.dark-mode header,
body.dark-mode nav,
body.dark-mode footer {
  background-color: #07121a;
  color: #e6eef6;
  border-color: #16232b;
}

/* section 卡片 —— 深色背景、柔和边框、去除强阴影以减低对比 */
body.dark-mode section {
  background-color: #0f1b24;
  color: #e6eef6;
  border: 1px solid #17282f;
  box-shadow: none;
}

/* 表单元素（输入框 / 下拉 / 文本域 / 按钮）的暗色样式 */
body.dark-mode input,
body.dark-mode select,
body.dark-mode textarea {
  background-color: #0b1620;
  color: #e6eef6;
  border: 1px solid #22333f;
  box-shadow: none;
}

/* 输入框获取焦点时的高亮 (适度可见) */
body.dark-mode input:focus,
body.dark-mode select:focus,
body.dark-mode textarea:focus {
  outline: none;
  border-color: #2b9bff;
  box-shadow: 0 0 0 4px rgba(43,155,255,0.10);
}

/* 按钮在暗色下保持可见（保留品牌色） */
body.dark-mode button {
  background-color: #2563eb;
  color: #fff;
  border: 1px solid rgba(255,255,255,0.06);
  box-shadow: 0 6px 16px rgba(37,99,235,0.12);
}

/* 结果显示框（确保可读） */
body.dark-mode #lengthResult,
body.dark-mode #areaResult,
body.dark-mode #volumeResult,
body.dark-mode #bmiResult,
body.dark-mode #tempResult,
body.dark-mode #timeResult {
  background-color: #07121a;
  color: #dff3ff;
  border: 1px solid #15232b;
}

/* 下拉菜单（嵌套菜单）背景 */
body.dark-mode nav ul ul {
  background-color: #07121a;
  border-color: #16232b;
}

/* 链接与占位符颜色 */
body.dark-mode a { color: #8fd1ff; }
body.dark-mode ::placeholder { color: #9fb4bf; opacity: 1; }

/* 细节：表格/小文本/标签 */
body.dark-mode label,
body.dark-mode .small-note {
  color: #bcd3de;
}

/*
body.dark-mode section,
body.dark-mode input,
body.dark-mode select,
body.dark-mode textarea {
  background-color: #0f1b24 !important;
  color: #e6eef6 !important;
  border-color: #17282f !important;
}
*/