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*{box-sizing:border-box}html{scroll-behavior:auto;scrollbar-gutter:stable}body{margin:0;background:var(--bg);color:var(--text);font:16px/1.6 var(--font)}button,a,input{font:inherit}button,a{-webkit-tap-highlight-color:transparent}a{color:inherit;text-decoration:none}button{color:inherit;cursor:pointer}button:disabled{cursor:default}button{border:0}button:focus-visible,a:focus-visible{outline:2px solid var(--accent);outline-offset:5px}svg{display:block}button,a{touch-action:manipulation}.sidebar{position:fixed;inset:0 auto 0 0;width:250px;background:var(--sidebar);border-right:1px solid var(--border);padding:32px 22px 22px;z-index:20;display:flex;flex-direction:column}.brand{display:flex;gap:12px;align-items:center;font-size:25px;font-weight:700;letter-spacing:-1px;line-height:1.25}.brand-sub{display:block;font-size:9px;font-weight:600;letter-spacing:2px;color:var(--muted);margin-top:7px}.course-label{border:1px solid 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@media(max-width:850px){.sidebar{transform:translateX(-100%);width:265px;transition:transform .2s}.sidebar.open{transform:translateX(0)}.scrim:not([hidden]){display:block;position:fixed;inset:0;background:#030710aa;z-index:19}.app-shell{margin-left:0}.menu-button{display:block;width:40px;height:44px;flex-shrink:0}.topbar{height:70px;padding:0 22px;justify-content:flex-start}.course-chip{margin-left:auto}.topbar-name{font-size:10px;letter-spacing:1px}.topbar-name span{margin:0 8px}.intro h1{font-size:38px}.intro-meta strong{font-size:28px}main{padding:28px 24px 38px}.nav-link{min-height:48px}.sidebar-bottom{padding-bottom:env(safe-area-inset-bottom)}.chapter-banner h1{font-size:33px}.sidebar{padding-top:max(25px,env(safe-area-inset-top))}}
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@media(prefers-reduced-motion:reduce){html{scroll-behavior:auto}*,*::before,*::after{transition:none!important;animation:none!important}}

html{min-height:100%;padding-top:env(safe-area-inset-top);padding-bottom:env(safe-area-inset-bottom)}
@media(pointer:coarse){button,.text-link{min-height:44px}a,button{touch-action:manipulation}input,select{font-size:16px}}
@media(max-width:850px){.simulation-frame{height:80dvh;min-height:480px}.workspace-bar{flex-wrap:wrap;gap:12px}.topbar{height:auto;min-height:70px}.theme-toggle{flex-shrink:0}}
.lesson-row[href="#/lessons/9"] .lesson-number{font-size:14px;white-space:nowrap}

/* Reserve the embedded scene while it starts, avoiding a white flash or reflow. */
.simulation-viewport{position:relative;background:var(--bg)}
.simulation-loading{position:absolute;inset:0;display:grid;place-items:center;color:var(--muted);font-size:14px;background:var(--bg)}
.simulation-frame[aria-busy=true]{visibility:hidden}

/* Close the mobile menu immediately when a new page is selected. */
.sidebar:not(.open){transition:none}

/* Keep the prepared browsing context connected; reparenting reloads an iframe. */
#page-view{outline:0}
.simulation-workspace.is-preparing{position:fixed;left:-20000px;top:0;width:var(--preparation-width,900px);pointer-events:none}
.simulation-workspace[hidden]{display:none}

.simulation-workspace .simulation-frame{visibility:visible}
.simulation-workspace .simulation-loading{z-index:1}