/* ================================================================
   BUTLER — Introduction Website
   ================================================================ */

/* -------- Custom Properties -------- */
:root{
  --bg-primary:    #0f1117;
  --bg-secondary:  #1a1d27;
  --bg-surface:    #242836;
  --border:        #2e3348;

  --primary:       #6c8cff;
  --primary-hover: #8ba4ff;
  --primary-glow:  rgba(108,140,255,.15);
  --accent-purple: #a78bfa;
  --accent-green:  #4ade80;
  --danger:        #ff5c6c;

  --text-primary:    #e8eaf0;
  --text-secondary:  #8b8fa8;
  --text-on-primary: #ffffff;

  --font-sans: 'Inter','Noto Sans JP','Helvetica Neue',Arial,'Hiragino Kaku Gothic ProN',sans-serif;
  --font-mono: 'Fira Code','Source Code Pro',monospace;

  --section-pad: 6rem;
  --card-pad:    2rem;
  --max-w:       1100px;
  --header-h:    64px;
}

/* -------- Reset -------- */
*,*::before,*::after{margin:0;padding:0;box-sizing:border-box}
html{scroll-behavior:smooth;scroll-padding-top:var(--header-h)}
body{
  font-family:var(--font-sans);
  font-size:1rem;line-height:1.8;
  color:var(--text-primary);
  background:var(--bg-primary);
  -webkit-font-smoothing:antialiased;
  overflow-x:hidden;
}
a{color:var(--primary);text-decoration:none;transition:color .2s}
a:hover{color:var(--primary-hover)}
img,svg{display:block;max-width:100%}
code{
  font-family:var(--font-mono);font-size:.875rem;
  background:var(--bg-surface);padding:.12em .4em;border-radius:4px;
}

/* -------- Utility -------- */
.container{width:100%;max-width:var(--max-w);margin:0 auto;padding:0 1.5rem}
.section{padding:var(--section-pad) 0}
.section--alt{background:var(--bg-secondary)}

/* Section Heading */
.section-heading{text-align:center;margin-bottom:3rem}
.section-heading__bar{
  display:block;width:48px;height:3px;
  background:var(--primary);border-radius:2px;
  margin:0 auto 1rem;
}
.section-heading h2{font-size:2rem;font-weight:700;line-height:1.3}

/* ================================================================
   HEADER
   ================================================================ */
.site-header{
  position:sticky;top:0;z-index:1000;
  background:rgba(15,17,23,.85);
  backdrop-filter:blur(12px);-webkit-backdrop-filter:blur(12px);
  border-bottom:1px solid transparent;
  transition:border-color .3s;
}
.site-header.scrolled{border-bottom-color:var(--border)}

.header-inner{
  display:flex;align-items:center;justify-content:space-between;
  max-width:var(--max-w);margin:0 auto;
  padding:0 1.5rem;height:var(--header-h);
}

/* Logo */
.logo-link{display:flex;align-items:center;gap:.6rem;color:var(--text-primary);flex-shrink:0}
.logo-img{height:50px;}
.logo-text{font-size:1.25rem;font-weight:700;letter-spacing:.08em}

/* Nav */
.nav-list{display:flex;list-style:none;gap:.25rem}
.nav-link{
  display:inline-block;padding:.5rem .75rem;
  font-size:.875rem;font-weight:500;
  color:var(--text-secondary);
  border-bottom:2px solid transparent;
  transition:color .2s,border-color .2s;
}
.nav-link:hover,.nav-link.active{color:var(--primary);border-bottom-color:var(--primary)}

/* Hamburger */
.menu-toggle{display:none;background:0 0;border:0;color:var(--text-primary);cursor:pointer;padding:.25rem}
.hamburger-icon .bar{transition:transform .3s,opacity .3s}

/* Drawer overlay */
.drawer-overlay{display:none;position:fixed;inset:0;background:rgba(0,0,0,.55);z-index:998}
.drawer-overlay.open{display:block}

/* ================================================================
   HERO
   ================================================================ */
.hero{
  position:relative;display:flex;align-items:center;justify-content:center;
  min-height:90vh;text-align:center;overflow:hidden;
}
.hero-glow{
  position:absolute;top:-20%;left:50%;transform:translateX(-50%);
  width:800px;height:800px;
  background:radial-gradient(circle,var(--primary-glow) 0%,transparent 70%);
  pointer-events:none;
}
.hero-content{position:relative;z-index:1;padding:2rem 1.5rem}

.hero-logo-wrap{height:120px;margin:0 auto 2rem;overflow:hidden}
.hero-logo{
  width:100%;height:100%;object-fit:cover;
  animation:pulse-glow 3s ease-in-out infinite;
}
@keyframes pulse-glow{
  0%,100%{filter:drop-shadow(0 0 14px rgba(108,140,255,.35))}
  50%    {filter:drop-shadow(0 0 28px rgba(108,140,255,.6))}
}

.hero-title{font-size:3rem;font-weight:700;line-height:1.2;letter-spacing:.1em;margin-bottom:.75rem}
.hero-subtitle{font-size:1rem;color:var(--text-secondary);margin-bottom:1.5rem;letter-spacing:.02em}
.hero-catch{
  font-size:1.1rem;line-height:1.9;
  max-width:640px;margin:0 auto 2.5rem;
}

/* CTA */
.btn-cta{
  display:inline-block;padding:.875rem 2rem;
  background:var(--primary);color:var(--text-on-primary);
  font-size:1rem;font-weight:600;border:0;border-radius:8px;
  cursor:pointer;transition:background .3s,transform .3s;
}
.btn-cta:hover{background:var(--primary-hover);color:var(--text-on-primary);transform:translateY(-2px)}

/* ================================================================
   OVERVIEW
   ================================================================ */
.overview-body{max-width:780px;margin:0 auto 3rem}
.overview-body p{margin-bottom:1rem}
.overview-body p:last-child{margin-bottom:0}

.info-cards{display:grid;grid-template-columns:repeat(4,1fr);gap:1.5rem}

.info-card{
  background:var(--bg-surface);border:1px solid var(--border);
  border-radius:12px;padding:var(--card-pad);text-align:center;
  transition:transform .3s,box-shadow .3s;
}
.info-card:hover{transform:translateY(-4px);box-shadow:0 8px 32px rgba(108,140,255,.1)}
.info-card__icon{margin:0 auto 1rem;display:flex;justify-content:center}
.info-card__kw{display:block;font-size:1.125rem;font-weight:700;color:var(--primary);margin-bottom:.4rem}
.info-card__desc{font-size:.875rem;color:var(--text-secondary);line-height:1.6}

/* ================================================================
   FEATURES
   ================================================================ */
.feat-grid{display:grid;grid-template-columns:repeat(2,1fr);gap:1.5rem}

.feat-card{
  background:var(--bg-surface);border:1px solid var(--border);
  border-radius:12px;padding:var(--card-pad);
  transition:transform .3s,box-shadow .3s;
}
.feat-card:hover{transform:translateY(-4px);box-shadow:0 8px 32px rgba(108,140,255,.1)}
.feat-card__icon{margin-bottom:1rem}
.feat-card__title{font-size:1.25rem;font-weight:600;line-height:1.4;margin-bottom:.5rem}
.feat-card__desc{font-size:.9375rem;color:var(--text-secondary);line-height:1.7}

/* ================================================================
   FLOW
   ================================================================ */
.flow-track{display:grid;grid-template-columns:repeat(4,1fr);gap:2rem;position:relative}

.flow-card{
  position:relative;
  background:var(--bg-surface);border:1px solid var(--border);
  border-radius:12px;padding:var(--card-pad);text-align:center;
  transition:transform .3s,box-shadow .3s;
}
.flow-card:hover{transform:translateY(-4px);box-shadow:0 8px 32px rgba(108,140,255,.1)}

/* connector (desktop) */
.flow-card:not(:last-child)::after{
  content:'';position:absolute;
  top:50%;right:calc(-2rem);
  width:2rem;height:2px;
  background:rgba(108,140,255,.3);
  pointer-events:none;
}

.flow-card__num{
  display:inline-flex;align-items:center;justify-content:center;
  width:40px;height:40px;border-radius:50%;
  background:var(--primary);color:var(--text-on-primary);
  font-weight:700;font-size:1rem;margin-bottom:1rem;
}
.flow-card__title{font-size:1.125rem;font-weight:600;margin-bottom:.5rem}
.flow-card__desc{font-size:.875rem;color:var(--text-secondary);line-height:1.6;margin-bottom:.75rem}

.flow-card__notes{list-style:none;text-align:left}
.flow-card__notes li{
  font-size:.8125rem;color:var(--text-secondary);line-height:1.5;
  padding-left:1em;position:relative;margin-bottom:.25rem;
}
.flow-card__notes li::before{content:'·';position:absolute;left:0;color:var(--primary);font-weight:700}

/* ================================================================
   TECH
   ================================================================ */
.tech-cols{display:grid;grid-template-columns:1fr 1fr;gap:2rem;align-items:start}

/* styled table (shared with requirements) */
.styled-table-wrap{overflow-x:auto}
.styled-table{
  width:100%;border-collapse:collapse;
  background:var(--bg-surface);border:1px solid var(--border);
  border-radius:12px;overflow:hidden;font-size:.9375rem;
}
.styled-table thead tr{background:var(--primary);color:var(--text-on-primary)}
.styled-table th,.styled-table td{padding:.75rem 1rem;text-align:left}
.styled-table th{font-weight:600;white-space:nowrap}
.styled-table tbody tr{border-bottom:1px solid var(--border)}
.styled-table tbody tr:last-child{border-bottom:0}
.styled-table tbody tr:hover{background:rgba(108,140,255,.04)}

/* file tree */
.file-tree-wrap{
  background:var(--bg-surface);border:1px solid var(--border);
  border-radius:12px;overflow:hidden;
}
.file-tree-label{
  padding:.75rem 1.25rem;font-size:.875rem;
  font-weight:600;color:var(--text-secondary);
  border-bottom:1px solid var(--border);
}
.file-tree{
  margin:0;padding:1.5rem 1.25rem;
  border-left:3px solid var(--primary);
  margin-left:1rem;overflow-x:auto;
  font-size:.875rem;line-height:1.6;
  color:var(--text-primary);background:transparent;
}
.file-tree code{background:0 0;padding:0;font-size:inherit}

/* ================================================================
   API
   ================================================================ */
.api-stack{display:flex;flex-direction:column;gap:2rem}

.api-card{
  background:var(--bg-surface);border:1px solid var(--border);
  border-radius:12px;padding:var(--card-pad);
  transition:transform .3s,box-shadow .3s;
}
.api-card:hover{transform:translateY(-4px);box-shadow:0 8px 32px rgba(108,140,255,.1)}

.api-card__head{display:flex;align-items:center;gap:.75rem;flex-wrap:wrap;margin-bottom:.75rem}
.api-badge{
  display:inline-block;padding:.2em .6em;border-radius:4px;
  font-size:.75rem;font-weight:700;letter-spacing:.05em;text-transform:uppercase;
}
.api-badge--post{background:rgba(74,222,128,.15);color:var(--accent-green)}
.api-path{font-family:var(--font-mono);font-size:1rem;font-weight:600;background:0 0;padding:0}

.api-card__desc{font-size:.9375rem;color:var(--text-secondary);line-height:1.7;margin-bottom:1.25rem}

.api-card__pair{display:grid;grid-template-columns:1fr 1fr;gap:1rem}
.api-card__label{
  font-size:.75rem;font-weight:600;color:var(--text-secondary);
  text-transform:uppercase;letter-spacing:.06em;margin-bottom:.5rem;
}
.api-card__block pre{
  background:var(--bg-primary);border:1px solid var(--border);
  border-radius:8px;padding:1rem 1.25rem;
  overflow-x:auto;margin:0;font-size:.8125rem;line-height:1.6;
}
.api-card__block pre code{background:0 0;padding:0;font-size:inherit}

/* ================================================================
   SECURITY
   ================================================================ */
.sec-list{max-width:800px;margin:0 auto;display:flex;flex-direction:column;gap:2rem}
.sec-row{display:flex;align-items:flex-start;gap:1.25rem}

.sec-row__icon{
  flex-shrink:0;width:48px;height:48px;
  display:flex;align-items:center;justify-content:center;
  background:var(--bg-surface);border:1px solid var(--border);border-radius:10px;
}
.sec-row__body h3{font-size:1.0625rem;font-weight:600;margin-bottom:.375rem}
.sec-row__body p{font-size:.9375rem;color:var(--text-secondary);line-height:1.7}

/* ================================================================
   REQUIREMENTS
   ================================================================ */
.req-wrap{max-width:720px;margin:0 auto}

/* ================================================================
   FOOTER
   ================================================================ */
.site-footer{
  background:var(--bg-secondary);border-top:1px solid var(--border);
  padding:2rem 1.5rem;text-align:center;
}
.footer-inner{max-width:var(--max-w);margin:0 auto}
.footer-brand{
  display:inline-flex;align-items:center;gap:.5rem;
  font-weight:700;font-size:1rem;color:var(--text-secondary);margin-bottom:.5rem;
}
.footer-brand img{width:24px;height:24px;border-radius:50%}
.footer-version,.footer-copy{font-size:.8125rem;color:var(--text-secondary);margin-bottom:.25rem}

/* ================================================================
   SCROLL ANIMATION
   ================================================================ */
.fade-up{
  opacity:0;transform:translateY(24px);
  transition:opacity .6s ease,transform .6s ease;
}
.fade-up.is-visible{opacity:1;transform:translateY(0)}

/* ================================================================
   RESPONSIVE — Tablet (≤ 1023px)
   ================================================================ */
@media(max-width:1023px){
  :root{--max-w:90vw}

  .info-cards{grid-template-columns:repeat(2,1fr)}
  .flow-track{grid-template-columns:repeat(2,1fr)}
  .flow-card:not(:last-child)::after{display:none}
  .tech-cols{grid-template-columns:1fr}
  .api-card__pair{grid-template-columns:1fr}
}

/* ================================================================
   RESPONSIVE — Mobile (≤ 600px)
   ================================================================ */
@media(max-width:600px){
  :root{--section-pad:4rem;--card-pad:1.25rem}

  .container{padding:0 1rem}

  /* hamburger */
  .menu-toggle{display:block}

  .main-nav{
    position:fixed;top:0;right:0;
    width:280px;height:100vh;
    background:var(--bg-secondary);
    transform:translateX(100%);transition:transform .3s ease;
    z-index:999;padding:5rem 1.5rem 2rem;overflow-y:auto;
  }
  .main-nav.open{transform:translateX(0)}
  .nav-list{flex-direction:column;gap:0}
  .nav-link{
    display:block;padding:.875rem 0;font-size:1rem;
    border-bottom:1px solid var(--border);border-left:0;
  }

  /* hero */
  .hero{min-height:70vh}
  .hero-logo-wrap{width:90px;height:90px}
  .hero-title{font-size:2rem}
  .hero-subtitle{font-size:.875rem}
  .hero-catch{font-size:.9375rem}

  .section-heading h2{font-size:1.5rem}
  .info-cards{grid-template-columns:repeat(2,1fr);gap:1rem}
  .feat-grid{grid-template-columns:1fr}
  .flow-track{grid-template-columns:1fr;gap:1.5rem}

  /* flow vertical connectors */
  .flow-card:not(:last-child)::after{
    display:block;
    top:auto;bottom:-1.5rem;left:50%;right:auto;
    width:2px;height:1.5rem;
    transform:translateX(-50%);
  }

  .api-card__pair{grid-template-columns:1fr}
}

@media(max-width:400px){
  .info-cards{grid-template-columns:1fr}
}