:root{
  --bg:#f5f7fb;
  --bg2:#edf4ff;
  --panel:#ffffff;
  --ink:#102033;
  --muted:#5b687c;
  --line:#dde6f2;
  --brand:#1557d9;
  --brand2:#0f3e9b;
  --accent:#00a86b;
  --accent2:#29d39a;
  --dark:#0f172a;
  --code:#0b1220;
  --codeText:#f3f7ff;
  --soft:#edf4ff;
  --gold:#f5b942;
  --shadow:0 22px 55px rgba(17,34,68,.12);
  --radius:24px;
}
*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{
  margin:0;
  font-family:Arial, Helvetica, sans-serif;
  color:var(--ink);
  background:
    radial-gradient(circle at top left, rgba(21,87,217,.14), transparent 35%),
    linear-gradient(180deg,#f0f6ff 0%,#f8fbff 42%,#fff 100%);
  line-height:1.68;
}
a{color:var(--brand);text-decoration:none}
a:hover{text-decoration:underline}
img{max-width:100%}
.skip-link{
  position:absolute;left:-999px;top:auto;width:1px;height:1px;overflow:hidden;
}
.skip-link:focus{
  left:16px;top:16px;width:auto;height:auto;background:#fff;padding:10px 14px;border-radius:10px;z-index:999;
}
.topbar{
  background:#0f172a;
  color:#d7e3f8;
  font-size:.86rem;
}
.topbar-inner{
  width:min(1200px,calc(100% - 32px));
  margin:auto;
  display:flex;
  justify-content:space-between;
  align-items:center;
  gap:14px;
  padding:8px 0;
}
.topbar a{color:#fff;font-weight:700}
.site-header{
  position:sticky;
  top:0;
  z-index:80;
  background:rgba(255,255,255,.95);
  border-bottom:1px solid var(--line);
  backdrop-filter:blur(14px);
}
.header-inner{
  width:min(1200px,calc(100% - 32px));
  margin:auto;
  min-height:74px;
  display:flex;
  justify-content:space-between;
  align-items:center;
  gap:18px;
}
.brand{
  display:flex;
  gap:12px;
  align-items:center;
  color:var(--ink);
}
.logo{
  width:42px;height:42px;border-radius:13px;
  background:linear-gradient(135deg,var(--brand),#6aa4ff);
  display:grid;place-items:center;color:#fff;font-weight:900;
  box-shadow:0 12px 24px rgba(21,87,217,.24);
}
.brand-text strong{display:block;font-size:1.05rem;line-height:1.1}
.brand-text span{display:block;color:var(--muted);font-size:.84rem}
.nav{
  display:flex;
  gap:16px;
  align-items:center;
  flex-wrap:wrap;
}
.nav a{font-weight:700;color:var(--ink);font-size:.94rem}
.nav .cta{color:#fff}
.menu-toggle{
  display:none;
  border:1px solid var(--line);
  background:#fff;
  color:var(--ink);
  border-radius:12px;
  padding:8px 11px;
  font-size:1.25rem;
}
.btn,.btn-outline,.btn-light,.mini-btn{
  display:inline-flex;
  align-items:center;
  justify-content:center;
  gap:8px;
  border-radius:999px;
  font-weight:800;
  text-decoration:none;
  transition:transform .16s ease,box-shadow .16s ease,background .16s ease,border .16s ease;
}
.btn{
  padding:13px 20px;
  background:linear-gradient(135deg,var(--brand),#2f76ff);
  color:#fff;
  box-shadow:0 14px 28px rgba(21,87,217,.25);
}
.btn-outline{
  padding:12px 18px;
  border:1px solid #b9c9e4;
  background:#fff;
  color:var(--brand2);
}
.btn-light{
  padding:12px 18px;
  background:#fff;
  color:var(--brand2);
}
.mini-btn{
  padding:9px 13px;
  background:var(--brand);
  color:#fff;
  font-size:.9rem;
}
.btn:hover,.btn-outline:hover,.btn-light:hover,.mini-btn:hover{
  transform:translateY(-1px);
  text-decoration:none;
}
.hero{
  width:min(1200px,calc(100% - 32px));
  margin:42px auto 28px;
  display:grid;
  grid-template-columns:1.35fr .9fr;
  gap:26px;
  align-items:stretch;
}
.hero-main,.hero-side{
  border:1px solid var(--line);
  border-radius:var(--radius);
  box-shadow:var(--shadow);
  overflow:hidden;
}
.hero-main{
  background:
    linear-gradient(135deg,rgba(255,255,255,.96),rgba(245,249,255,.98)),
    radial-gradient(circle at top right,rgba(41,211,154,.18),transparent 35%);
  padding:clamp(28px,5vw,58px);
}
.eyebrow{
  display:inline-flex;
  align-items:center;
  gap:8px;
  background:var(--soft);
  color:var(--brand2);
  border:1px solid #d6e4ff;
  border-radius:999px;
  padding:6px 12px;
  font-weight:900;
  font-size:.82rem;
  text-transform:uppercase;
  letter-spacing:.04em;
}
h1{
  font-size:clamp(2.2rem,4.4vw,4.5rem);
  line-height:1.04;
  margin:18px 0;
  letter-spacing:-.04em;
}
h2{
  font-size:clamp(1.55rem,2.4vw,2.35rem);
  line-height:1.2;
  letter-spacing:-.02em;
  margin:0 0 16px;
}
h3{font-size:1.16rem;margin:20px 0 8px}
.lead{
  color:var(--muted);
  font-size:1.13rem;
  max-width:780px;
}
.hero-actions{display:flex;gap:12px;flex-wrap:wrap;margin-top:24px}
.trust-row{
  display:grid;
  grid-template-columns:repeat(4,1fr);
  gap:12px;
  margin-top:28px;
}
.trust-item{
  background:#fff;
  border:1px solid var(--line);
  border-radius:18px;
  padding:14px;
}
.trust-item strong{display:block;color:var(--ink)}
.trust-item span{display:block;color:var(--muted);font-size:.92rem}
.hero-side{
  background:linear-gradient(160deg,#0e244d 0%,#1557d9 100%);
  color:#fff;
  padding:24px;
  position:relative;
}
.hero-side:before{
  content:"";
  position:absolute;
  width:240px;height:240px;border-radius:50%;
  background:rgba(255,255,255,.12);
  right:-80px;top:-80px;
}
.book-cover{
  display:block;
  width:min(230px,72%);
  margin:0 auto 20px;
  border-radius:12px;
  box-shadow:0 22px 38px rgba(0,0,0,.35);
  position:relative;
}
.hero-side h2,.hero-side p,.book-actions,.book-bullets{position:relative}
.hero-side p{color:rgba(255,255,255,.88)}
.book-bullets{
  margin:16px 0;
  padding:0;
  list-style:none;
  display:grid;
  gap:7px;
}
.book-bullets li:before{content:"✓ ";color:#9cf4cf;font-weight:900}
.book-actions{display:flex;gap:10px;flex-wrap:wrap}
.wrap{
  width:min(1200px,calc(100% - 32px));
  margin:0 auto 46px;
}
.section{
  background:var(--panel);
  border:1px solid var(--line);
  border-radius:var(--radius);
  box-shadow:0 12px 30px rgba(17,34,68,.07);
  padding:clamp(22px,4vw,40px);
  margin-bottom:24px;
}
.section-head{
  display:flex;
  justify-content:space-between;
  gap:20px;
  align-items:end;
  margin-bottom:20px;
}
.section-head p{color:var(--muted);max-width:740px;margin:0}
.path-grid{
  display:grid;
  grid-template-columns:repeat(4,1fr);
  gap:16px;
}
.path-card{
  border:1px solid var(--line);
  background:linear-gradient(180deg,#fff,#f9fbff);
  border-radius:20px;
  padding:20px;
  min-height:205px;
}
.path-badge{
  display:inline-block;
  border-radius:999px;
  background:#eaf8f2;
  color:#08784f;
  padding:5px 10px;
  font-size:.78rem;
  font-weight:900;
}
.lesson-grid{
  display:grid;
  grid-template-columns:repeat(3,1fr);
  gap:16px;
}
.lesson-card{
  display:flex;
  flex-direction:column;
  min-height:238px;
  border:1px solid var(--line);
  border-radius:20px;
  padding:20px;
  background:#fff;
  color:var(--ink);
  transition:transform .16s ease,box-shadow .16s ease,border-color .16s ease;
}
.lesson-card:hover{
  transform:translateY(-3px);
  box-shadow:0 18px 34px rgba(17,34,68,.1);
  border-color:#b8c9e7;
  text-decoration:none;
}
.lesson-number{
  color:var(--accent);
  font-weight:900;
  font-size:.82rem;
  text-transform:uppercase;
  letter-spacing:.05em;
}
.lesson-card p{
  color:var(--muted);
  margin-bottom:auto;
}
.card-link{font-weight:900;margin-top:16px;color:var(--brand)}
.feature-band{
  display:grid;
  grid-template-columns:1fr 1fr;
  gap:18px;
}
.feature-card{
  border-radius:22px;
  border:1px solid var(--line);
  padding:24px;
  background:linear-gradient(135deg,#f8fbff,#fff);
}
.feature-list{
  margin:14px 0 0;
  padding:0;
  list-style:none;
  display:grid;
  gap:9px;
}
.feature-list li:before{content:"✓ ";font-weight:900;color:var(--accent)}
.author-card{
  display:grid;
  grid-template-columns:1.3fr .7fr;
  gap:22px;
  align-items:center;
  background:linear-gradient(135deg,#0f172a,#173a7a);
  color:#fff;
  border-radius:var(--radius);
  padding:clamp(24px,4vw,38px);
}
.author-card p{color:#dbe8ff}
.author-links{display:flex;gap:10px;flex-wrap:wrap}
.layout{
  width:min(1200px,calc(100% - 32px));
  margin:32px auto 48px;
  display:grid;
  grid-template-columns:285px 1fr;
  gap:24px;
  align-items:start;
}
.sidebar{
  position:sticky;
  top:96px;
  background:#fff;
  border:1px solid var(--line);
  border-radius:22px;
  box-shadow:0 12px 30px rgba(17,34,68,.07);
  padding:18px;
}
.sidebar h3{margin-top:0}
.lesson-nav{
  display:grid;
  gap:6px;
  max-height:61vh;
  overflow:auto;
  padding-right:4px;
}
.lesson-nav a{
  color:var(--ink);
  border-radius:12px;
  padding:8px 10px;
  font-size:.92rem;
}
.lesson-nav a.active,.lesson-nav a:hover{
  background:var(--soft);
  color:var(--brand2);
  text-decoration:none;
}
.side-promo{
  margin-top:18px;
  border-top:1px solid var(--line);
  padding-top:18px;
}
.side-promo img{
  width:88px;
  border-radius:8px;
  box-shadow:0 8px 18px rgba(0,0,0,.16);
}
.content{
  background:#fff;
  border:1px solid var(--line);
  border-radius:var(--radius);
  box-shadow:var(--shadow);
  padding:clamp(24px,4vw,48px);
}
.breadcrumb{
  color:var(--muted);
  font-size:.93rem;
  margin-bottom:12px;
}
.lesson-meta{
  display:flex;
  gap:10px;
  flex-wrap:wrap;
  margin:18px 0 24px;
}
.badge{
  border-radius:999px;
  padding:6px 10px;
  background:#eef4ff;
  color:var(--brand2);
  font-size:.84rem;
  font-weight:900;
}
.callout{
  border-left:5px solid var(--brand);
  border-radius:16px;
  padding:16px 18px;
  background:#f8fbff;
  margin:24px 0;
}
.note-box{
  background:#f7fffb;
  border:1px solid #caeadb;
  border-radius:16px;
  padding:18px;
  margin:24px 0;
}
.note-box ul{margin:8px 0 0}
pre{
  position:relative;
  background:var(--code);
  color:var(--codeText);
  border-radius:18px;
  padding:48px 18px 18px;
  overflow:auto;
  font-size:.95rem;
  line-height:1.55;
  box-shadow:inset 0 1px 0 rgba(255,255,255,.05);
}
code{font-family:"Courier New", Courier, monospace}
.copy-btn{
  position:absolute;
  top:12px;
  right:12px;
  border:1px solid rgba(255,255,255,.24);
  background:rgba(255,255,255,.1);
  color:#fff;
  border-radius:999px;
  padding:6px 12px;
  cursor:pointer;
  font-weight:800;
}
.practice{
  background:#fffaf0;
  border:1px solid #f3d69b;
  border-radius:18px;
  padding:18px;
  margin:24px 0;
}
.lesson-promo{
  display:grid;
  grid-template-columns:110px 1fr auto;
  gap:18px;
  align-items:center;
  background:linear-gradient(100deg,#f3f8ff,#fff);
  border:1px solid var(--line);
  border-radius:22px;
  padding:18px;
  margin:28px 0;
}
.lesson-promo img{
  width:92px;
  border-radius:8px;
  box-shadow:0 8px 18px rgba(0,0,0,.18);
}
.lesson-promo p{margin:.25rem 0 0;color:var(--muted)}
.prev-next{
  display:flex;
  justify-content:space-between;
  gap:14px;
  border-top:1px solid var(--line);
  padding-top:24px;
  margin-top:34px;
}
.prev-next a{
  background:#f8fbff;
  border:1px solid var(--line);
  border-radius:14px;
  color:var(--ink);
  padding:12px 14px;
  font-weight:900;
}
.related{
  display:grid;
  grid-template-columns:repeat(3,1fr);
  gap:12px;
  margin-top:20px;
}
.related a{
  border:1px solid var(--line);
  border-radius:16px;
  padding:14px;
  background:#fff;
  color:var(--ink);
  font-weight:800;
}
.site-footer{
  background:#0f172a;
  color:#d9e5f8;
  padding:40px 0;
}
.footer-inner{
  width:min(1200px,calc(100% - 32px));
  margin:auto;
  display:grid;
  grid-template-columns:1.2fr 1fr 1fr;
  gap:22px;
}
.footer-inner h3{margin-top:0;color:#fff}
.footer-inner a{color:#fff}
.footer-links{
  display:grid;
  gap:8px;
}
.copyright{
  grid-column:1/-1;
  border-top:1px solid rgba(255,255,255,.16);
  padding-top:18px;
  color:#aebbd2;
}
@media(max-width:980px){
  .menu-toggle{display:inline-flex}
  .nav{
    display:none;
    position:absolute;
    top:74px;
    left:16px;
    right:16px;
    background:#fff;
    border:1px solid var(--line);
    box-shadow:var(--shadow);
    border-radius:20px;
    padding:16px;
    flex-direction:column;
    align-items:stretch;
  }
  .nav.open{display:flex}
  .topbar-inner{flex-direction:column;align-items:flex-start}
  .hero,.layout,.author-card,.feature-band{grid-template-columns:1fr}
  .trust-row,.path-grid,.lesson-grid,.related{grid-template-columns:1fr}
  .sidebar{position:static}
  .lesson-promo{grid-template-columns:1fr;text-align:center}
  .lesson-promo img{margin:auto}
  .prev-next{flex-direction:column}
  .footer-inner{grid-template-columns:1fr}
}
@media(max-width:560px){
  h1{font-size:2.15rem}
  .header-inner{min-height:68px}
  .brand-text span{display:none}
  .hero{margin-top:24px}
  .hero-main{padding:24px}
}

.book-feature-section{
  background:
    radial-gradient(circle at top right, rgba(21,87,217,.10), transparent 35%),
    linear-gradient(135deg,#ffffff,#f7fbff);
}
.book-feature-grid{
  display:grid;
  grid-template-columns:260px 1fr;
  gap:28px;
  align-items:center;
}
.book-feature-cover{
  text-align:center;
}
.book-feature-cover img{
  width:min(230px,100%);
  border-radius:14px;
  box-shadow:0 22px 42px rgba(15,23,42,.25);
}
.book-feature-copy h3{
  font-size:1.7rem;
  margin-top:0;
}
@media(max-width:980px){
  .book-feature-grid{
    grid-template-columns:1fr;
    text-align:center;
  }
  .book-feature-copy .feature-list{
    text-align:left;
  }
}