/* =========================================================
   TKHJ Tools - Light Editorial (SaaS Education)
   ========================================================= */

:root{
  --indigo:#4F46E5;
  --violet:#7C3AED;
  --grad:linear-gradient(135deg,#4F46E5,#7C3AED);

  --bg:#FFFFFF;
  --surface:#F9FAFB;
  --surface-2:#F3F4F6;
  --card:#FFFFFF;
  --ai-bg:#F5F3FF;

  --line:#E5E7EB;
  --line-strong:#D1D5DB;

  --text-1:#111827;
  --text-2:#6B7280;
  --text-3:#9CA3AF;

  --brand:#3B82F6;
  --brand-dark:#1D4ED8;

  --chatgpt:#059669;
  --notion:#1F2937;
  --gemini:#2563EB;
  --prompt:#7C3AED;
  --workflow:#7C3AED;
  --productivity:#F59E0B;

  --radius-lg:16px;
  --radius-md:12px;
  --radius-pill:999px;
  --shadow-1:0 1px 2px rgba(0,0,0,.04);
  --shadow-2:0 4px 16px rgba(0,0,0,.06);
  --shadow-hover:0 8px 24px rgba(0,0,0,.08);
}

/* ============ DARK THEME ============ */
[data-theme="dark"]{
  --bg:#0B0F19;
  --surface:#131826;
  --surface-2:#1B2030;
  --card:#161C2B;
  --ai-bg:#131826;

  --line:rgba(255,255,255,.08);
  --line-strong:rgba(255,255,255,.14);

  --text-1:#F3F4F6;
  --text-2:#9CA3AF;
  --text-3:#6B7280;

  --brand:#60A5FA;
  --brand-dark:#3B82F6;

  --shadow-1:0 1px 2px rgba(0,0,0,.4);
  --shadow-2:0 4px 16px rgba(0,0,0,.3);
  --shadow-hover:0 8px 24px rgba(124,58,237,.18);
}

*{box-sizing:border-box}
html,body{margin:0;padding:0}
body{
  background:var(--bg); color:var(--text-2);
  font-family:Inter,system-ui,-apple-system,sans-serif;
  font-size:15px;line-height:1.65;
  -webkit-font-smoothing:antialiased;letter-spacing:-.003em;
  transition:background .25s,color .25s;
}
a{text-decoration:none;color:inherit}
img{display:block;max-width:100%}
button{font-family:inherit;cursor:pointer;border:none;background:none}
input{font-family:inherit}
ul{list-style:none;padding:0;margin:0}
.container{width:100%;max-width:1200px;margin:0 auto;padding:0 28px}

/* THEME TOGGLE BUTTON */
.theme-toggle{
  width:38px;height:38px;border-radius:50%;
  display:inline-flex;align-items:center;justify-content:center;
  color:var(--text-2);transition:background .15s,color .15s;
  flex-shrink:0;
}
.theme-toggle:hover{background:var(--surface-2);color:var(--text-1)}
.theme-toggle svg{width:18px;height:18px;stroke:currentColor;fill:none;stroke-width:2}
.theme-toggle .icon-sun{display:none}
[data-theme="dark"] .theme-toggle .icon-sun{display:block}
[data-theme="dark"] .theme-toggle .icon-moon{display:none}

/* TOP NAV */
.site-header{
  position:sticky;top:0;z-index:100;
  background:color-mix(in srgb,var(--bg) 85%,transparent);
  backdrop-filter:blur(16px) saturate(180%);
  -webkit-backdrop-filter:blur(16px) saturate(180%);
  border-bottom:1px solid var(--line);
  transition:border-color .2s,box-shadow .2s;
}
.site-header.scrolled{box-shadow:var(--shadow-1)}
.nav-row{height:64px;display:flex;align-items:center;justify-content:space-between;gap:24px}

.brand{font-weight:800;font-size:1.35rem;color:var(--text-1);letter-spacing:-.01em;display:flex;align-items:center;gap:4px;text-decoration:none}
.brand .dot{color:var(--brand);font-size:1.6rem;line-height:1;margin-left:-2px}
.brand svg{height:28px;width:auto;display:block}

.nav-links{display:flex;gap:4px}
.nav-links a{
  padding:9px 18px;border-radius:var(--radius-pill);
  color:var(--text-2);font-weight:500;font-size:.95rem;
  transition:background .15s,color .15s;
}
.nav-links a:hover{background:var(--surface-2);color:var(--text-1)}
.nav-links a.active{background:var(--text-1);color:var(--bg);font-weight:600}
[data-theme="dark"] .nav-links a.active{background:var(--brand);color:#fff}

.nav-right{display:flex;align-items:center;gap:12px;margin-left:auto}

/* HERO */
.hero{padding:72px 0 64px;text-align:center;background:var(--surface)}
.hero h1{
  font-size:clamp(2rem,4.5vw,3rem);line-height:1.1;
  color:var(--text-1);margin:0 0 16px;letter-spacing:-.02em;font-weight:800;
}
.hero p.lead{color:var(--text-2);font-size:1.08rem;max-width:560px;margin:0 auto 28px}
.hero-search{
  max-width:520px;margin:0 auto;
  display:flex;align-items:center;gap:6px;
  background:var(--card);border:1px solid var(--line);
  border-radius:var(--radius-pill);padding:8px 8px 8px 20px;
  box-shadow:var(--shadow-2);
}
.hero-search input{
  flex:1;border:none;background:none;outline:none;
  color:var(--text-1);font-size:1rem;
}
.hero-search input::placeholder{color:var(--text-3)}
.hero-search button{
  padding:10px 22px;border-radius:var(--radius-pill);
  background:var(--text-1);color:var(--bg);font-weight:600;font-size:.92rem;
  transition:background .15s;
}
.hero-search button:hover{background:var(--brand-dark)}

/* SECTIONS */
.section{padding:72px 0;background:var(--bg)}
.section-ai{padding:72px 0;background:var(--ai-bg)}

.section-head{display:flex;align-items:flex-end;justify-content:space-between;gap:20px;margin-bottom:28px;flex-wrap:wrap}
.section-head .title-wrap{display:flex;flex-direction:column;gap:6px}
.section-head h2{margin:0;font-size:clamp(1.4rem,2.4vw,1.8rem);color:var(--text-1);letter-spacing:-.015em;font-weight:800}
.section-head .sub{margin:0;color:var(--text-2);font-size:.95rem}

/* View-all outline CTA */
.view-all{
  display:inline-flex;align-items:center;gap:6px;
  padding:10px 22px;border-radius:var(--radius-pill);
  border:1.5px solid var(--brand);color:var(--brand);
  background:transparent;font-size:.9rem;font-weight:600;
  transition:background .15s,color .15s;
}
.view-all:hover{background:var(--brand);color:#fff}
[data-theme="dark"] .view-all:hover{color:#fff}

/* Filter tabs */
.tabs{display:flex;gap:8px;margin-bottom:28px;flex-wrap:wrap}
.tab{
  padding:8px 18px;border-radius:var(--radius-pill);
  background:var(--card);color:var(--text-2);font-size:.88rem;font-weight:500;
  border:1px solid var(--line);cursor:pointer;
  transition:background .15s,color .15s,border-color .15s;
}
.tab:hover{border-color:var(--brand);color:var(--text-1)}
.tab.active{background:var(--brand);color:#fff;border-color:var(--brand)}
[data-theme="dark"] .tab.active{color:#fff}

/* 4-COL GRID */
.grid-4{display:grid;gap:20px;grid-template-columns:repeat(1,1fr)}
@media(min-width:600px){.grid-4{grid-template-columns:repeat(2,1fr)}}
@media(min-width:860px){.grid-4{grid-template-columns:repeat(3,1fr)}}
@media(min-width:1100px){.grid-4{grid-template-columns:repeat(4,1fr)}}

/* ARTICLE CARD */
.card{
  position:relative;background:var(--card);
  border:1px solid var(--line);border-radius:var(--radius-lg);
  overflow:hidden;display:flex;flex-direction:column;
  transition:transform .15s ease,box-shadow .15s ease,border-color .15s ease;
  box-shadow:var(--shadow-1);
}
.card:hover{transform:translateY(-4px);box-shadow:var(--shadow-hover);border-color:var(--line-strong)}

.card-body{padding:16px 18px 18px;display:flex;flex-direction:column;gap:8px;flex:1}

.card-meta{display:flex;align-items:center;gap:10px;font-size:.76rem;color:var(--text-3)}

.card-cat{
  display:inline-flex;align-items:center;gap:4px;
  padding:4px 10px;border-radius:var(--radius-pill);
  font-size:.72rem;font-weight:700;letter-spacing:.04em;
  text-transform:uppercase;align-self:flex-start;
}

.cat-cet4{background:#EFF6FF;color:#2563EB}
.cat-cet6{background:#EFF6FF;color:#1D4ED8}
.cat-ielts{background:#F5F3FF;color:#7C3AED}
.cat-toefl{background:#EEF2FF;color:#4338CA}
.cat-gre{background:#EEF2FF;color:#4338CA}
.cat-sat{background:#EEF2FF;color:#3730A3}
.cat-chatgpt{background:#ECFDF5;color:#059669}
.cat-notion{background:#F3F4F6;color:#1F2937}
.cat-gemini{background:#EFF6FF;color:#2563EB}
.cat-prompt{background:#F5F3FF;color:#7C3AED}
.cat-workflow{background:#F5F3FF;color:#7C3AED}
.cat-productivity{background:#FFFBEB;color:#D97706}
.cat-ai{background:#F5F3FF;color:#7C3AED}

[data-theme="dark"] .cat-cet4{background:rgba(59,130,246,.15);color:#60A5FA}
[data-theme="dark"] .cat-cet6{background:rgba(37,99,235,.15);color:#60A5FA}
[data-theme="dark"] .cat-ielts{background:rgba(124,58,237,.15);color:#A78BFA}
[data-theme="dark"] .cat-toefl{background:rgba(99,102,241,.15);color:#A78BFA}
[data-theme="dark"] .cat-gre{background:rgba(79,70,229,.15);color:#A78BFA}
[data-theme="dark"] .cat-sat{background:rgba(67,56,202,.15);color:#A78BFA}
[data-theme="dark"] .cat-chatgpt{background:rgba(16,185,129,.15);color:#34D399}
[data-theme="dark"] .cat-notion{background:rgba(243,244,246,.1);color:#F3F4F6}
[data-theme="dark"] .cat-gemini{background:rgba(96,165,250,.15);color:#60A5FA}
[data-theme="dark"] .cat-prompt{background:rgba(139,92,246,.15);color:#A78BFA}
[data-theme="dark"] .cat-workflow{background:rgba(124,58,237,.15);color:#A78BFA}
[data-theme="dark"] .cat-productivity{background:rgba(251,191,36,.15);color:#FBBF24}
[data-theme="dark"] .cat-ai{background:rgba(124,58,237,.15);color:#A78BFA}

.card-title{font-size:1.02rem;line-height:1.4;color:var(--text-1);font-weight:700;margin:0;display:-webkit-box;-webkit-line-clamp:2;-webkit-box-orient:vertical;overflow:hidden;letter-spacing:-.005em}
.card-desc{font-size:.88rem;color:var(--text-2);margin:0;display:-webkit-box;-webkit-line-clamp:2;-webkit-box-orient:vertical;overflow:hidden;line-height:1.55}
.card-foot{margin-top:auto;display:flex;align-items:center;justify-content:space-between;font-size:.78rem;color:var(--text-3);padding-top:12px;border-top:1px solid var(--line)}

.card-cover{
  width:100%;padding:14px 18px;
  background:linear-gradient(135deg,#EEF2FF,#F5F3FF);
  border-bottom:1px solid var(--line);
  color:var(--brand);font-size:.78rem;font-weight:700;
  text-transform:uppercase;letter-spacing:.08em;
}
[data-theme="dark"] .card-cover{
  background:linear-gradient(135deg,rgba(79,70,229,.18),rgba(124,58,237,.14));
  color:var(--brand);
}

/* AI card COPY button */
.copy-btn{
  display:inline-flex;align-items:center;gap:4px;
  padding:6px 12px;border-radius:var(--radius-md);
  border:1px solid var(--line);background:var(--card);
  color:var(--text-2);font-size:.78rem;font-weight:600;
  cursor:pointer;transition:all .15s;
}
.copy-btn:hover{border-color:var(--brand);color:var(--text-1)}
.copy-btn.copied{border-color:var(--chatgpt);color:var(--chatgpt)}

/* CTA row */
.cta-row{margin-top:36px;text-align:center}

/* FOOTER */

/* ARTICLE DETAIL PAGE */
.article-hero{padding:56px 0 24px;border-bottom:1px solid var(--line);background:var(--surface)}
.article-hero .tag{
  font-size:.72rem;font-weight:700;letter-spacing:.08em;text-transform:uppercase;
  color:var(--brand);margin-bottom:12px;display:inline-block;
}
.article-hero h1{font-size:clamp(1.8rem,4vw,2.4rem);line-height:1.2;margin:0 0 14px;color:var(--text-1);letter-spacing:-.02em;font-weight:800}
.article-hero .meta{display:flex;gap:16px;color:var(--text-2);font-size:.88rem;flex-wrap:wrap}
.article-hero .meta span+span::before{content:"•";margin-right:12px;color:var(--text-3)}
.article-body{max-width:740px;margin:0 auto;padding:48px 24px 32px}
.article-body h2{margin:40px 0 16px;font-weight:800;color:var(--text-1);font-size:1.4rem;letter-spacing:-.01em}
.article-body h3{margin:32px 0 12px;font-weight:700;color:var(--text-1);font-size:1.15rem}
.article-body p{margin:0 0 20px;line-height:1.75}
.article-body ul,.article-body ol{padding-left:22px;margin:0 0 20px}
.article-body li{margin-bottom:6px}
.article-body strong{color:var(--text-1)}
.article-body blockquote{border-left:3px solid var(--brand);padding:6px 20px;margin:28px 0;color:var(--text-1);background:var(--surface);border-radius:0 12px 12px 0}
.article-body code{background:var(--surface-2);padding:2px 8px;border-radius:6px;font-size:.88em;color:var(--text-1)}
.article-body table{width:100%;border-collapse:collapse;margin:24px 0 30px}
.article-body th,.article-body td{border:1px solid var(--line);padding:10px 14px;text-align:left}
.article-body th{background:var(--surface)}
.article-foot{max-width:740px;margin:0 auto;padding:24px 24px 56px;display:flex;align-items:center;justify-content:space-between;border-top:1px solid var(--line)}
.article-foot a{color:var(--brand);font-weight:600;font-size:.9rem}

/* HELPERS */
.sr-only{position:absolute;left:-9999px;width:1px;height:1px;overflow:hidden}
.ttip{position:relative}
.hidden{display:none!important}

[data-theme="dark"] .brand img{filter:invert(1) hue-rotate(180deg)}

/* Theme toggle icons: sun shown in light, moon shown in dark */
.theme-toggle .icon-sun{display:inline}
.theme-toggle .icon-moon{display:none}
[data-theme="dark"] .theme-toggle .icon-sun{display:none}
[data-theme="dark"] .theme-toggle .icon-moon{display:inline}
.site-footer{
  background:var(--surface);border-top:1px solid var(--line);
  margin-top:80px;padding:48px 0 32px;
}
.foot-grid{display:grid;grid-template-columns:2fr 1fr 1fr;gap:40px}
.foot-col h4{margin:0 0 12px;font-size:.85rem;font-weight:700;letter-spacing:.04em;text-transform:uppercase;color:var(--text-2)}
.foot-col a{display:block;color:var(--text-2);font-size:.92rem;line-height:1.8;text-decoration:none}
.foot-col a:hover{color:var(--brand)}
.foot-col p{margin:0;font-size:.88rem;color:var(--text-3);line-height:1.6}
.foot-copy{text-align:center;font-size:.82rem;color:var(--text-3);margin-top:40px;padding-top:24px;border-top:1px solid var(--line)}

/* Search input - expand on focus */
.nav-search{display:flex;align-items:center;padding:0;margin:0;background:transparent;border:none}
.nav-search input{padding:10px;width:120px;border:none;outline:none;border-radius:5px;box-shadow:0 1px gray;font-size:18px;transition:width .3s;font-family:Consolas,monaco,monospace;background:var(--surface);color:var(--text-1)}
.nav-search input:focus{outline:1px solid var(--brand);box-shadow:none;width:230px}
.nav-search input::placeholder{color:var(--brand)}