:root{--bg:#1b1b2f;--surface:#25253f;--surface-2:#2d2d4c;--line:#3f3f66;--line-strong:#6e6eaa;--line-soft:#34345a;--track:#3a3a5c;--text:#eee;--text-2:#cfcde3;--muted:#b7b4cf;--green:#3fcf7a;--green-hover:#8ff0a0;--on-green:#1b1b2f;--green-ink:#8ff0a0;--green-ink-hover:#c9ffd0;--purple:#7a3fc2;--purple-dark:#55299a;--purple-ink:#c9b3f2;--on-purple:#e6dbf7;--on-purple-bright:#fff;--on-accent:#eee;--locked-login-title:#fff;--gold:#ffd84a;--gold-ink:#ffd84a;--error:#ff5fa2;--focus:#ffd84a;--grid-bg:#25253f;--grid-text:#eee;--grid-line:#3f3f66;--grid-head:#2d2d4c;--grid-head-text:#b7b4cf;--grid-head-line:#3f3f66;--grid-head-sel:#3f3f66;--grid-head-sel-text:#eee;--grid-active:#eee;--grid-sel:#eeeeee14;--grid-anchor:#eeeeee14;--grid-ref:#7a3fc238;--grid-point:#c9b3f2;--editor-bg:#2d2d4c;--editor-text:#8ff0a0;--target-line:#ffd84a;--target-fill:inset 0 0 0 0 transparent;--pass-line:#3fcf7a;--pass-line-width:2px;--pass-fill:#3fcf7a29;--pass-text:#c9ffd0;--pivot-cell:#7a3fc214;--vis-green:#3fcf7a;--vis-purple:#c9b3f2;--vis-pink:#ff5fa2;--vis-gold:#ffd84a;--banner-bg:#25253f;--banner-text:#eee;--banner-link:#ffd84a;--banner-line:#34345a;--banner-close:#cfcde3;--shadow-strong:#00000073;--shadow-mid:#0006;--shadow-soft:#00000059;--dot-ring:#ffffff40;--bug-fill:#c9ffd0;--trail:#a0e6ff8c;--panel-green:#3fcf7a;--panel-green-hover:#8ff0a0;--panel-on-green:#1b1b2f;--font-wordmark:"Pixelify Sans", ui-monospace, monospace;--font-display:"Space Grotesk", system-ui, sans-serif;--font-body:Inter, system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;--font-mono:"JetBrains Mono", ui-monospace, "SF Mono", Consolas, monospace;--radius:6px;--radius-card:10px;--header-h:65px;color-scheme:dark;font-family:var(--font-body);color:var(--text);background:var(--bg);font-size:16px;line-height:1.5}:root[data-theme=light]{--bg:#f6f5fb;--surface:#fff;--surface-2:#eeecf6;--line:#d9d6e8;--line-strong:#8582a8;--line-soft:#e6e3f0;--track:#dddaea;--text:#1b1b2f;--text-2:#3f3d5c;--muted:#5d5a7c;--green:#107c41;--green-hover:#0e6b38;--on-green:#fff;--green-ink:#0e6b38;--green-ink-hover:#0a5229;--purple-ink:#6a32b0;--on-accent:#fff;--locked-login-title:#1b1b2f;--gold-ink:#9c5700;--error:#9c0006;--focus:#7a3fc2;--grid-bg:#fff;--grid-text:#1b1b2f;--grid-line:#e1e1e1;--grid-head:#f5f5f5;--grid-head-text:#616161;--grid-head-line:#d4d4d4;--grid-head-sel:#d3f0e0;--grid-head-sel-text:#0e5c2f;--grid-active:#107c41;--grid-sel:#1b1b2f12;--grid-anchor:transparent;--grid-ref:#7a3fc224;--grid-point:#7a3fc2;--editor-bg:#fff;--editor-text:#1b1b2f;--target-line:#b26b00;--target-fill:inset 0 0 0 99px #ffeb9c;--pass-line:#6fbf7f;--pass-line-width:1px;--pass-fill:#c6efce;--pass-text:#006100;--pivot-cell:#7a3fc20f;--vis-green:#107c41;--vis-purple:#6a32b0;--vis-pink:#b8124f;--vis-gold:#9c5700;--banner-bg:#55299a;--banner-text:#fff;--banner-line:#55299a;--banner-close:#e6dbf7;--shadow-strong:#28245029;--shadow-mid:#28245024;--shadow-soft:#2824501f;--dot-ring:#1b1b2f33;--trail:#288cc88c;color-scheme:light}.pass-panel,.locked-panel:not(.locked-login),.banner.launch{--green:var(--panel-green);--green-hover:var(--panel-green-hover);--on-green:var(--panel-on-green);--focus:var(--gold)}*{box-sizing:border-box}body{background:var(--bg);color:var(--text);overflow-wrap:break-word;flex-direction:column;min-height:100vh;margin:0;display:flex}h1,h2,h3{font-family:var(--font-display);letter-spacing:-.01em;font-weight:700;line-height:1.15}a{color:var(--green-ink)}a:hover{color:var(--green-ink-hover)}:focus-visible{outline:2px solid var(--focus);outline-offset:2px}button,summary,a{-webkit-tap-highlight-color:transparent}button{font:inherit;cursor:pointer;color:inherit}code,kbd,pre{font-family:var(--font-mono);font-variant-ligatures:none}code{color:var(--green-ink);background:var(--surface-2);overflow-wrap:anywhere;border-radius:4px;padding:1px 6px;font-size:.9em}kbd{color:var(--text);background:var(--surface-2);border:1px solid var(--line-strong);white-space:nowrap;border-radius:4px;padding:1px 6px;font-size:.85em}kbd.reserved{text-decoration:underline dotted var(--gold-ink);text-underline-offset:3px;cursor:help}strong{font-weight:600}.muted{color:var(--muted)}.small{font-size:13px}@media not ((hover:none) and (pointer:coarse)){.touch-only{display:none!important}}@media (hover:none) and (pointer:coarse){.kbd-only{display:none!important}body .formula-bar input,body .cell-editor,body .goal-seek-field input{font-size:16px}}.btn,.actions button,.key-row button{border-radius:var(--radius);border:1px solid var(--line-strong);min-height:44px;color:var(--text);box-shadow:none;background:0 0;justify-content:center;align-items:center;gap:6px;padding:0 18px;font-weight:500;text-decoration:none;display:inline-flex}.btn:hover,.actions button:hover{background:var(--surface-2);color:var(--text)}.btn-primary,.actions button.primary{background:var(--green);border-color:var(--green);color:var(--on-green);font-weight:700}.btn-primary:hover,.actions button.primary:hover{background:var(--green-hover);border-color:var(--green-hover);color:var(--on-green)}.btn-login{background:var(--purple);border-color:var(--purple);color:var(--on-accent);white-space:nowrap;flex-shrink:0;font-weight:700}.btn-login:hover{background:var(--purple-dark);border-color:var(--purple-dark);color:var(--on-accent)}.btn-lg{min-height:52px;padding:0 22px;font-size:17px}.actions button.ghost{color:var(--muted);border-color:#0000}.actions button.ghost:hover{color:var(--text);background:0 0;text-decoration:underline}button.link{color:var(--green-ink);font-size:inherit;background:0 0;border:0;min-height:0;padding:0;text-decoration:underline}.site-header{z-index:20;background:var(--bg);border-bottom:1px solid var(--line-soft);position:sticky;top:0}.header-inner{max-width:1360px;min-height:var(--header-h);justify-content:space-between;align-items:center;gap:16px;margin:0 auto;padding:12px 24px;display:flex}.brand{color:var(--text);flex-shrink:0;align-items:center;gap:10px;text-decoration:none;display:flex}.brand:hover{color:var(--text)}.brand svg{display:block}.wordmark{font-family:var(--font-wordmark);letter-spacing:.02em;font-size:22px;font-weight:700;line-height:1}.wordmark span{color:var(--green)}.main-nav{align-items:center;gap:22px;font-size:15px;display:flex}.main-nav>a:not(.btn){color:var(--text-2);text-decoration:none}.main-nav>a:not(.btn):hover{color:var(--text)}.phone-login{display:none}@media (width<=359px){.site-header .header-inner{gap:8px;padding:8px 12px}.brand{gap:6px}.header-inner .wordmark{font-size:16px}.header-inner .phone-login{padding:0 10px}}.menu{display:none;position:relative}.menu summary{border:1px solid var(--line-strong);background:var(--surface);cursor:pointer;border-radius:8px;place-items:center;width:44px;height:44px;list-style:none;display:grid}.menu summary::-webkit-details-marker{display:none}.menu[open] summary{background:var(--surface-2)}.menu-panel{background:var(--surface);border:1px solid var(--line);border-radius:var(--radius-card);width:min(320px,100vw - 32px);box-shadow:0 16px 40px var(--shadow-strong);flex-direction:column;gap:4px;max-height:calc(100dvh - 72px);padding:8px;display:flex;position:absolute;top:52px;right:0;overflow-y:auto}.menu-panel>a{color:var(--text);border-radius:var(--radius);min-height:44px;padding:12px;text-decoration:none}.menu-panel>a:hover{background:var(--surface-2);color:var(--text)}.more{position:relative}.more summary{color:var(--text-2);cursor:pointer;align-items:center;gap:6px;list-style:none;display:inline-flex}.more summary::-webkit-details-marker{display:none}.more summary:hover,.more[open] summary{color:var(--text)}.more[open] summary svg,.settings-chip.open svg{transform:rotate(180deg)}.more-panel{background:var(--surface);border:1px solid var(--line);border-radius:var(--radius-card);min-width:180px;box-shadow:0 16px 40px var(--shadow-strong);flex-direction:column;padding:6px;display:flex;position:absolute;top:calc(100% + 14px);left:-12px}.more-panel a{color:var(--text);border-radius:var(--radius);padding:10px 12px;text-decoration:none}.more-panel a:hover{background:var(--surface-2);color:var(--text)}.menu-label{font-family:var(--font-mono);font-variant-ligatures:none;letter-spacing:.04em;text-transform:uppercase;color:var(--muted);border-top:1px solid var(--line);margin-top:4px;padding:12px 12px 4px;font-size:11px}.top-controls{align-items:center;gap:18px;display:flex}.top-controls button{white-space:nowrap}.settings{position:relative}.settings-chip{border:1px solid var(--line-strong);border-radius:var(--radius);color:var(--text-2);background:0 0;align-items:center;gap:8px;min-height:34px;padding:6px 12px;font-size:13px;display:inline-flex}.settings-chip:hover,.settings-chip.open{background:var(--surface-2);color:var(--text)}.practice-dot{background:var(--purple);width:8px;height:8px;box-shadow:0 0 0 2px var(--dot-ring);border-radius:50%}.settings-panel{z-index:30;background:var(--surface);border:1px solid var(--line);border-radius:var(--radius-card);width:260px;box-shadow:0 16px 40px var(--shadow-strong);white-space:normal;flex-direction:column;gap:14px;padding:14px;display:flex;position:absolute;top:calc(100% + 12px);right:0}.setting{flex-direction:column;gap:6px;display:flex}.setting-label{font-family:var(--font-mono);font-variant-ligatures:none;text-transform:uppercase;letter-spacing:.06em;color:var(--muted);font-size:11px}.setting .segmented{display:flex}.setting .segmented button{flex:1}.settings-panel .practice-btn{align-self:stretch}.menu-panel .menu-controls{border-top:1px solid var(--line);flex-direction:column;align-items:stretch;gap:14px;margin-top:4px;padding:12px}.menu-controls .points{align-self:flex-start}.menu-controls .segmented button{min-height:44px;font-size:14px}.menu-controls .practice-btn{min-height:44px}.segmented{border:1px solid var(--line-strong);border-radius:var(--radius);display:inline-flex;overflow:hidden}.segmented button{color:var(--text-2);background:0 0;border:0;min-height:34px;padding:6px 12px;font-size:13px}.segmented button+button{border-left:1px solid var(--line-strong)}.segmented button.on{background:var(--surface-2);color:var(--text);box-shadow:inset 0 -2px 0 var(--green);font-weight:600}.segmented button{flex-direction:column;align-items:center;display:inline-flex}.segmented button:after{content:attr(data-label);visibility:hidden;height:0;font-weight:600;overflow:hidden}.practice-btn{border:1px solid var(--line-strong);border-radius:var(--radius);color:var(--text-2);background:0 0;min-height:34px;padding:6px 12px;font-size:13px}.practice-btn:hover{background:var(--surface-2)}.practice-btn.on{background:var(--purple);border-color:var(--purple);color:var(--on-purple-bright)}.points{font-family:var(--font-display);color:var(--gold-ink);white-space:nowrap;font-weight:600}.main-nav .points{text-align:right;font-variant-numeric:tabular-nums;min-width:11ch}@media (hover:none) and (pointer:coarse){.practice-btn{display:none}}.banner{border-bottom:1px solid var(--line-soft);background:var(--surface);padding:8px 24px;font-size:14px}.banner.ok{box-shadow:inset 3px 0 0 var(--green);color:var(--green-ink-hover)}.banner.warn{box-shadow:inset 3px 0 0 var(--gold-ink);color:var(--text-2)}.banner.launch{background:var(--banner-bg);color:var(--banner-text);border-bottom-color:var(--banner-line);box-shadow:inset 3px 0 0 var(--gold);align-items:center;gap:12px;display:flex}.banner.launch a{color:var(--banner-link);font-weight:600;text-decoration:none}.banner.launch a:hover{text-decoration:underline}.banner-close{min-width:32px;min-height:32px;color:var(--text-2);cursor:pointer;background:0 0;border:0;margin-left:auto;font-size:18px;line-height:1}.banner.launch .banner-close{color:var(--banner-close)}.banner.launch .banner-close:hover{color:var(--banner-text)}.banner-close:hover{color:var(--text)}.page-body{flex:1;width:100%}.with-sidebar{grid-template-columns:272px minmax(0,1fr);max-width:1440px;margin:0 auto;display:grid}main{min-width:0}.lesson-list{top:var(--header-h);max-height:calc(100vh - var(--header-h));border-right:1px solid var(--line-soft);align-self:start;padding:16px 12px;position:sticky;overflow-y:auto}.list-title{font-family:var(--font-mono);font-variant-ligatures:none;text-transform:uppercase;letter-spacing:.06em;color:var(--muted);margin:4px 8px 10px;font-size:12px;text-decoration:none;display:block}a.list-title:hover{color:var(--text)}.list-title.spaced{margin-top:20px}.lesson-item{color:var(--text);border:1px solid #0000;border-radius:8px;gap:12px;padding:10px;text-decoration:none;display:flex}.lesson-item:hover{background:var(--surface);color:var(--text)}.lesson-item.active{background:var(--surface);border-color:var(--line)}.lesson-item.open .lesson-name{color:var(--gold-ink)}.topic-lessons{border-left:1px solid var(--line-soft);margin:2px 0 6px 22px;padding-left:8px}.tick{width:26px;height:26px;font-family:var(--font-display);background:var(--surface-2);color:var(--muted);border:1px solid var(--line);border-radius:50%;flex-shrink:0;place-items:center;font-size:13px;font-weight:700;display:grid}.tick.done{background:var(--green);border-color:var(--green);color:var(--on-green)}.lesson-name{font-size:14px;font-weight:600;line-height:1.35;display:block}.lesson-summary{color:var(--muted);margin-top:3px;font-size:12px;line-height:1.4;display:block}.site-footer{border-top:1px solid var(--line-soft);margin-top:40px}.footer-inner{max-width:1160px;color:var(--muted);flex-wrap:wrap;justify-content:space-between;gap:12px 24px;margin:0 auto;padding:24px;font-size:14px;display:flex}.site-footer a{color:var(--muted);text-decoration:none}.site-footer a:hover{color:var(--text)}.footer-nav a,.main-nav{white-space:nowrap}@media (width<=1240px){.main-nav>.btn-primary{display:none}}@media (width<=1080px){:root{--header-h:61px}.header-inner{padding:8px 16px}.wordmark{font-size:19px}.main-nav{display:none}.menu{display:block}.phone-login{margin-left:auto;padding:0 14px;display:inline-flex}}@media (width<=900px){.with-sidebar{display:block}.lesson-list{display:none}.banner{padding:8px 16px}.banner.launch{padding:6px 8px 6px 16px;font-size:13px}.footer-inner{flex-direction:column-reverse;padding:20px;font-size:13px}}.section{max-width:1160px;margin:0 auto;padding:48px 24px}.section-title{margin:0 0 8px;font-size:34px}.section-lede{color:var(--text-2);max-width:680px;margin:0 0 28px;font-size:17px}.free-account-link{color:var(--purple-ink);text-underline-offset:3px;text-decoration:underline}.free-account-link:hover{color:var(--text)}.prose{max-width:680px}.not-found{align-items:center;gap:40px;min-height:52vh;display:flex}.not-found-wizard{flex:none;line-height:0}.not-found-code{font-family:var(--font-mono);color:var(--error);margin:0 0 6px;font-size:15px;font-weight:600}@media (width<=600px){.not-found{flex-direction:column;align-items:flex-start;gap:20px;min-height:0}.not-found-wizard svg{width:80px;height:64px}}.post-list{gap:16px;margin:0;padding:0;list-style:none;display:grid}.post-card{background:var(--surface);border:1px solid var(--line);border-radius:var(--radius-card);color:var(--text);flex-direction:column;gap:6px;padding:18px;text-decoration:none;display:flex}.post-card:hover{border-color:var(--line-strong);background:var(--surface-2);color:var(--text)}.post-card time,.post-meta{color:var(--muted);font-size:14px}.post-back{margin:0 0 12px;font-size:14px}.post-meta{margin:0 0 28px}.blog-post{font-size:17px;line-height:1.65}.blog-post h2{margin:36px 0 12px;font-size:24px}.blog-post li{margin:6px 0}.blog-post blockquote{border-left:3px solid var(--purple);color:var(--text-2);margin:20px 0;padding:4px 18px}.post-related{background:var(--surface);border:1px solid var(--line);border-radius:var(--radius-card);margin-top:40px;padding:18px 20px}.post-related h2{margin:0 0 8px;font-size:18px}.post-related ul{margin:0;padding-left:20px}.post-related .coming-soon{color:var(--muted)}.login-form{flex-wrap:wrap;align-items:flex-end;gap:10px 12px;margin:20px 0;display:flex}.login-form label{color:var(--text-2);flex-basis:100%;font-size:14px;font-weight:600}.login-form input[type=email]{min-width:0;min-height:44px;font:16px var(--font-body);color:var(--text);background:var(--surface);border:1px solid var(--line-strong);border-radius:var(--radius);flex:260px;padding:0 14px}.login-form input[type=email]:focus{outline:2px solid var(--purple-ink);outline-offset:1px}.login-form .btn{flex:none}.login-actions{flex-wrap:wrap;gap:12px;display:flex}.check{color:var(--text-2);cursor:pointer;align-items:flex-start;gap:10px;font-size:14px;line-height:1.5;display:flex}.login-form .check{flex-basis:100%;margin:4px 0;font-weight:400}.check input{width:18px;height:18px;accent-color:var(--purple);flex-shrink:0;margin:2px 0 0}@media (width<=600px){.login-form .btn,.login-actions .btn{flex:100%}}.hero{flex-wrap:wrap;align-items:center;gap:48px;max-width:1160px;margin:0 auto;padding:72px 24px 56px;display:flex}.hero-copy{flex:420px;min-width:0}.hero h1{letter-spacing:-.02em;margin:0 0 20px;font-size:60px;line-height:1.02}.hero-lede{color:var(--text-2);max-width:520px;margin:0 0 28px;font-size:19px}.hero-buttons{flex-wrap:wrap;gap:12px;display:flex}.hero-preview{flex:460px;min-width:0;position:relative}.preview-card{background:var(--surface);border:1px solid var(--line);box-shadow:0 24px 60px var(--shadow-strong);border-radius:12px;overflow:hidden}.preview-strip{background:var(--surface-2);border-bottom:1px solid var(--line);color:var(--muted);align-items:center;gap:8px;padding:10px 14px;font-size:13px;display:flex}.code-tag{background:var(--purple);color:var(--on-purple-bright);font-weight:600;font-family:var(--font-mono);font-variant-ligatures:none;border-radius:4px;padding:2px 8px;font-size:12px}.preview-points{color:var(--gold-ink);font-family:var(--font-mono);font-variant-ligatures:none;margin-left:auto}.preview-grid{width:100%}.preview-grid .cell{cursor:default}.preview-grid .head{font-weight:600}.hero-wizard{pointer-events:none;line-height:0;position:absolute;bottom:-84px;right:-28px}.lesson-cards{grid-template-columns:repeat(auto-fill,minmax(200px,1fr));gap:16px;margin:0;padding:0;list-style:none;display:grid}.lesson-card{background:var(--surface);border:1px solid var(--line);border-radius:var(--radius-card);height:100%;color:var(--text);gap:14px;padding:18px;text-decoration:none;display:flex}.lesson-card:hover{border-color:var(--line-strong);background:var(--surface-2);color:var(--text)}.card-body{flex-direction:column;flex:1;gap:10px;min-width:0;display:flex}.card-title{font-size:17px;font-weight:700;line-height:1.3}.card-summary{color:var(--muted);font-size:14px}.needs-kb{color:var(--muted);font-size:13px;font-family:var(--font-mono);font-variant-ligatures:none}.tag{font-family:var(--font-mono);font-variant-ligatures:none;letter-spacing:.02em;font-size:12px}.card-num{font-family:var(--font-display);flex-shrink:0;width:28px;font-size:26px;font-weight:700;line-height:1.1;display:none}.tag-short{display:none}.lesson-cards.two-digit .card-num{white-space:nowrap;width:40px}.topic-card .card-num{white-space:nowrap;width:46px}.access-open .tag,.access-open .card-num{color:var(--green-ink)}.access-login .tag,.access-login 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