/* System Design Fundamentals Styles */
*{margin:0;padding:0;box-sizing:border-box}
body{font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Roboto,sans-serif;background:#ecfeff;color:#164e63;line-height:1.7;padding:20px}
.chapter{max-width:900px;margin:0 auto;background:#fff;border-radius:12px;padding:40px;box-shadow:0 2px 12px rgba(8,145,178,.15)}
h1{color:#0e7490;font-size:1.8rem;margin-bottom:16px;border-bottom:3px solid #0891b2;padding-bottom:8px}
h2{color:#0e7490;font-size:1.3rem;margin:24px 0 8px}
h3{color:#0891b2;font-size:1.1rem;margin:18px 0 6px}
h4{color:#0e7490;font-size:1rem;margin:14px 0 4px}
p{margin-bottom:14px}
ul,ol{margin:10px 0 14px 24px}
li{margin-bottom:4px}
table{width:100%;border-collapse:collapse;margin:14px 0}
th,td{border:1px solid #a5f3fc;padding:8px 12px;text-align:left;font-size:.9rem}
th{background:#0891b2;color:#fff;font-weight:600}
td{background:#f0fdfa}
pre{background:#164e63;color:#cffafe;padding:14px 18px;border-radius:8px;overflow-x:auto;font-size:.85rem;margin:14px 0;tab-size:2}
code{background:#cffafe;padding:2px 6px;border-radius:4px;font-size:.88rem;color:#0e7490}
pre code{background:transparent;padding:0;color:inherit}
a{color:#0e7490;text-decoration:none}
a:hover{text-decoration:underline}
img{max-width:100%;display:block;margin:20px auto;border-radius:8px}
.toc{list-style:none;margin:8px 0 16px;padding:0}
.toc li{margin-bottom:8px;padding:10px 14px;background:#ecfeff;border-radius:8px;border-left:4px solid #0891b2}
.toc li a{display:block;font-weight:500}
.toc small{display:block;color:#5b8a8c;font-size:.8rem;margin-top:2px}
.exercise{background:#cffafe;border-left:4px solid #0891b2;padding:12px 16px;margin:18px 0;border-radius:0 8px 8px 0;font-size:.92rem}
.exercise strong{color:#0e7490}
.note{background:#fef9c3;border-left:4px solid #eab308;padding:12px 16px;margin:14px 0;border-radius:0 8px 8px 0;font-size:.9rem}
nav{display:flex;justify-content:space-between;margin-top:30px;padding-top:16px;border-top:1px solid #a5f3fc;flex-wrap:wrap;gap:8px}
nav a{background:#0891b2;color:#fff;padding:8px 18px;border-radius:6px;font-size:.88rem;font-weight:500;transition:background .2s}
nav a:hover{background:#0e7490;text-decoration:none}
nav span{flex:1}
@media(max-width:600px){.chapter{padding:20px 14px}nav a{font-size:.8rem;padding:6px 12px}}