@import url('https://fonts.googleapis.com/css2?family=DM+Sans:wght@400;500;600;700&family=IBM+Plex+Sans+Arabic:wght@400;500;600;700&display=swap');
:root{--ink:#07111f;--muted:#667684;--paper:#f7f8f5;--cyan:#75e5ff;--orange:#ffb259;--mint:#c9f56d;--line:rgba(7,17,31,.13);--display:'DM Sans',Arial,sans-serif;--arabic:'IBM Plex Sans Arabic','DM Sans',sans-serif}
*{box-sizing:border-box}html{scroll-behavior:smooth}body{margin:0;background:var(--paper);color:var(--ink);font-family:var(--arabic);line-height:1.8}.lesson-shell{width:min(1040px,calc(100% - 40px));margin:auto}.lesson-nav{display:flex;align-items:center;justify-content:space-between;padding:20px 0;border-bottom:1px solid var(--line)}.lesson-brand{display:flex;align-items:center;gap:10px;font-size:13px;font-weight:700}.brand-mark{display:grid;place-items:center;width:38px;height:38px;color:var(--paper);border-radius:50%;background:var(--ink);font:700 11px var(--display)}.back-link{color:var(--muted);font:11px var(--display);text-decoration:none}.back-link:hover{color:var(--ink)}.lesson-header{padding:80px 0 58px;max-width:830px}.kicker{display:inline-flex;align-items:center;gap:9px;color:#159ab2;font:600 11px var(--display);letter-spacing:1px;text-transform:uppercase}.kicker::before{content:'';width:8px;height:8px;border-radius:50%;background:var(--orange)}h1{max-width:820px;margin:20px 0 17px;font-size:clamp(42px,7vw,82px);line-height:1.04;letter-spacing:-4px}h1 em{color:#159ab2;font-style:normal}.lead{max-width:690px;margin:0;color:var(--muted);font-size:18px;line-height:1.9}.lesson-layout{display:grid;grid-template-columns:1fr 285px;gap:54px;align-items:start;padding-bottom:90px}.lesson-content{min-width:0}.lesson-content h2{margin:46px 0 12px;font-size:30px;line-height:1.2;letter-spacing:-1px}.lesson-content h2:first-child{margin-top:0}.lesson-content h3{margin:28px 0 8px;font-size:20px}.lesson-content p{margin:0 0 16px;color:#566674;font-size:15px;line-height:2}.lesson-content ul{margin:0;padding:0 19px 0 0;color:#566674}.lesson-content li{margin:9px 0;padding-inline-start:6px}.formula{display:flex;align-items:center;justify-content:center;min-height:110px;margin:24px 0;padding:18px;color:var(--ink);border:1px solid rgba(7,17,31,.12);border-radius:18px;background:linear-gradient(135deg,#dff8fc,#fff4df);font:600 28px var(--display);direction:ltr}.example{margin:25px 0;padding:23px;border-inline-start:4px solid var(--cyan-deep);border-radius:0 14px 14px 0;background:#e9f4f2}.example strong{display:block;margin-bottom:5px;font-size:14px}.example p{margin:0;font-size:14px}.lesson-sidebar{position:sticky;top:22px;padding:20px;border:1px solid var(--line);border-radius:20px;background:#eef2ee}.sidebar-title{margin:0 0 16px;font:700 12px var(--display);letter-spacing:.5px}.sidebar-list{display:grid;gap:11px;margin:0;padding:0;list-style:none}.sidebar-list li{display:flex;gap:10px;color:var(--muted);font-size:12px;line-height:1.5}.sidebar-list li::before{content:'↗';color:#159ab2;font-family:var(--display)}details{margin-top:25px;border:1px solid var(--line);border-radius:14px;background:white}summary{padding:15px 18px;cursor:pointer;font-weight:600;font-size:14px}details p{padding:0 18px 17px;margin:0!important;font-size:13px!important}.lesson-footer{display:flex;align-items:center;justify-content:space-between;gap:18px;padding:24px 0 35px;border-top:1px solid var(--line);color:var(--muted);font:11px var(--display)}.footer-link{color:var(--ink);text-decoration:none}.footer-link:hover{color:#159ab2}.note{margin-top:33px;padding:14px 16px;color:#536572;border:1px solid rgba(27,185,214,.25);border-radius:13px;background:rgba(117,229,255,.12);font-size:12px;line-height:1.7}@media(max-width:760px){.lesson-shell{width:min(100% - 30px,590px)}.lesson-header{padding:53px 0 40px}.lesson-layout{grid-template-columns:1fr;gap:35px}.lesson-sidebar{position:static;order:-1}.lesson-content h2{font-size:26px}.formula{font-size:23px}.lesson-footer{align-items:flex-start;flex-direction:column}}