*{box-sizing:border-box}

html{scroll-behavior:smooth}

body{

    margin:0;

    font-family:Arial,Helvetica,sans-serif;

    background:#f6f8fc;

    color:#172033;

    line-height:1.75;

}

a{text-decoration:none;color:inherit}



.header{

    background:#fff;

    border-bottom:1px solid #e6ebf2;

    position:sticky;

    top:0;

    z-index:20;

}

.nav{

    max-width:1100px;

    margin:auto;

    padding:16px 22px;

    display:flex;

    justify-content:space-between;

    align-items:center;

    gap:20px;

}

.brand{

    font-weight:800;

    letter-spacing:.4px;

}

.brand small{

    display:block;

    font-size:11px;

    color:#687386;

    font-weight:600;

}

.back{

    font-size:14px;

    color:#2457c5;

    font-weight:700;

}



.hero{

    background:linear-gradient(135deg,#10284d,#1d4f91);

    color:#fff;

    padding:72px 22px;

}

.hero-inner{

    max-width:900px;

    margin:auto;

}

.badge{

    display:inline-block;

    padding:7px 12px;

    border:1px solid rgba(255,255,255,.35);

    border-radius:999px;

    font-size:12px;

    letter-spacing:1px;

    font-weight:700;

}

h1{

    font-size:48px;

    line-height:1.18;

    margin:18px 0;

}

.hero p{

    max-width:760px;

    font-size:18px;

    color:#dce8f7;

}



.container{

    max-width:900px;

    margin:auto;

    padding:50px 22px 70px;

}

.card{

    background:#fff;

    border:1px solid #e5eaf2;

    border-radius:18px;

    padding:30px;

    margin-bottom:24px;

    box-shadow:0 8px 24px rgba(20,40,70,.04);

}

h2{

    line-height:1.3;

    margin-top:0;

    font-size:28px;

}

h3{

    line-height:1.35;

}

ul{

    padding-left:22px;

}

li{

    margin-bottom:9px;

}

.highlight{

    background:#eef5ff;

    border-left:4px solid #2b6de0;

    padding:18px 20px;

    border-radius:8px;

    margin:22px 0;

}

.warning{

    background:#fff8e8;

    border-left:4px solid #d99a1d;

    padding:18px 20px;

    border-radius:8px;

    margin:22px 0;

}

.formula{

    background:#172033;

    color:#fff;

    padding:20px;

    border-radius:12px;

    text-align:center;

    font-weight:700;

    margin:20px 0;

}

.related{

    display:grid;

    grid-template-columns:repeat(2,1fr);

    gap:14px;

}

.related a{

    display:block;

    padding:17px;

    border:1px solid #e2e8f0;

    border-radius:12px;

    background:#fafcff;

    color:#2457c5;

    font-weight:700;

}

footer{

    background:#101b2d;

    color:#d7deea;

    text-align:center;

    padding:32px 20px;

    font-size:14px;

}

footer a{

    color:#fff;

    font-weight:700;

}



@media(max-width:700px){

    h1{font-size:35px}

    .hero{padding:55px 20px}

    .card{padding:22px}

    .related{grid-template-columns:1fr}

}

.table-of-contents{

  margin:24px 0;

  border:1px solid #e1e6ee;

  border-radius:12px;

  background:#f8fafc;

  overflow:hidden;

}



.toc-toggle{

  width:100%;

  border:0;

  background:#071b35;

  color:#fff;

  padding:16px 18px;

  font-size:16px;

  font-weight:700;

  display:flex;

  justify-content:space-between;

  align-items:center;

  cursor:pointer;

}



.toc-arrow{

  font-size:18px;

  line-height:1;

}



.toc-content{

  display:none;

  padding:14px 22px;

}



.table-of-contents.open .toc-content{

  display:block;

}



.toc-content ul{

  margin:0;

  padding-left:18px;

}



.toc-content li{

  margin:10px 0;

}



.toc-content a{

  color:#0d3b66;

  text-decoration:none;

  font-weight:600;

}



.toc-content a:hover{

  text-decoration:underline;

}



@media(max-width:600px){

  .toc-toggle{

    padding:15px;

  }



  .toc-content{

    padding:12px 18px;

  }

}

.author-box{

    margin:30px 0;

    padding:20px;

    border:1px solid #ddd;

    border-radius:10px;

    background:#f8f9fa;

}

.author-box strong{

    display:block;

    font-size:18px;

    margin-bottom:5px;

}

.author-box span{

    display:block;

    font-size:14px;

    margin-bottom:12px;

    color:#555;

}

.author-box p{

    margin:0;

    line-height:1.6;

}