/* A quiet, editorial layout keeps attention on the actual maths lessons. */
:root{--paper:#f7f5ee;--ink:#202e29;--muted:#3e4c45;--line:#d9dcd2;--blue:#2458d6;--serif:Georgia,'Times New Roman',serif;--sans:'Segoe UI',Arial,sans-serif}
*{box-sizing:border-box}html{scroll-behavior:smooth;scroll-padding-top:35px}body{margin:0;background:var(--paper);color:var(--ink);font-family:var(--sans);-webkit-font-smoothing:antialiased}a{color:inherit;text-decoration:none}a:focus-visible,video:focus-visible{outline:3px solid var(--blue);outline-offset:6px}.wrap{width:min(1200px,calc(100% - 112px));margin-inline:auto}.skip{position:absolute;top:-100px;left:20px;background:var(--ink);color:white;padding:12px;z-index:3}.skip:focus{top:10px}.navigation{height:110px;display:flex;align-items:center;justify-content:space-between;border-bottom:1px solid var(--line)}.wordmark{font-size:27px;font-weight:650;letter-spacing:-1.3px}.wordmark span{font-weight:400}.wordmark i{color:var(--blue);font-style:normal}.navigation nav{display:flex;gap:40px;font-size:14px}.navigation nav a:hover,.footer>a:last-child:hover{color:var(--blue)}.navigation nav span{margin-left:8px}.hero{display:grid;grid-template-columns:1.1fr 1fr;gap:48px;align-items:center;padding-top:91px;padding-bottom:100px}.eyebrow{font-size:11px;font-weight:650;letter-spacing:1.7px;display:flex;gap:10px;align-items:center;margin:0 0 27px}.status-dot{display:inline-block;width:7px;height:7px;border-radius:50%;background:var(--blue);flex:none}h1{font-family:var(--serif);font-size:clamp(45px,5.25vw,74px);font-weight:400;letter-spacing:-3.2px;line-height:1.09;margin:0 0 25px}h1 em{color:var(--blue);font-weight:400}.intro{font-size:17px;line-height:1.8;max-width:440px;color:var(--muted);margin:0 0 30px}.primary{display:inline-flex;align-items:center;gap:35px;background:var(--ink);color:var(--paper);padding:17px 22px;border-radius:3px;font-size:14px;transition:background .2s}.primary:hover{background:var(--blue)}.primary span{font-size:21px}.hero-note{font-size:12px;color:var(--muted);margin:17px 0 0}.illustration{padding-top:20px;transform:none}.figure-top,.figure-bottom{display:flex;align-items:center;justify-content:space-between;border-top:1px solid #bfc9bf;padding:16px 0}.figure-top{font-size:9px;letter-spacing:1.5px;color:var(--muted)}.illustration svg{width:100%;height:auto;display:block}.figure-bottom{padding-top:13px}.figure-caption{font-family:var(--serif);font-style:italic;font-size:17px}.figure-cross{font-size:26px;color:var(--blue)}.lessons{padding-bottom:60px}.section-heading{display:flex;justify-content:space-between;align-items:end;border-top:1px solid var(--ink);padding-top:34px;padding-bottom:44px}.section-heading .eyebrow{margin-bottom:17px}h2{font-family:var(--serif);font-size:43px;font-weight:400;line-height:1.17;letter-spacing:-1.3px;margin:0}.section-heading>p{font-size:14px;line-height:1.8;color:var(--muted);margin:0 0 4px}.lesson{display:grid;grid-template-columns:.8fr 1.2fr;gap:75px;padding:46px 0 50px;border-top:1px solid var(--line);align-items:center}.lesson-number{font-family:var(--serif);font-size:21px;color:var(--blue)}.lesson-number span{font-family:var(--sans);font-size:10px;letter-spacing:1.4px;color:var(--muted);margin-left:10px}h3{font-family:var(--serif);font-size:37px;font-weight:400;letter-spacing:-.9px;line-height:1.14;margin:22px 0 17px}.lesson-copy>p{max-width:340px;color:var(--muted);font-size:15px;line-height:1.8;margin:0}.topic-tags{display:flex;gap:8px;flex-wrap:wrap;margin:23px 0}.topic-tags span{border:1px solid var(--line);padding:6px 9px;border-radius:3px;font-size:11px;color:#536159}.lesson-copy>.lesson-detail{font-size:11px;line-height:1.7;color:#7b827b}.player{margin:0;min-width:0}.player video{display:block;width:100%;aspect-ratio:16/9;background:#0b1521;border-radius:4px;box-shadow:0 9px 24px #263d2910}.player figcaption{display:flex;justify-content:space-between;gap:15px;padding:15px 0 0;font-size:9px;letter-spacing:1px;color:var(--muted)}.player figcaption>span:last-child{letter-spacing:0;font-size:11px}.next{background:#e9ede3;border-block:1px solid #dbe1d3;padding:64px 0 68px}.next-inner{display:grid;grid-template-columns:1.1fr 1fr;gap:75px}.next .eyebrow{font-size:10px}.next h2{font-size:46px}.next-copy>p{font-size:16px;line-height:1.8;margin:0 0 18px;max-width:400px;color:#526054}.next ul{list-style:none;padding:0;margin:15px 0 22px}.next li{font-size:13px;border-bottom:1px solid #cfd7c8;padding:14px 0}.next li span{font-family:var(--serif);font-style:italic;color:#7c8c75;margin-right:18px}.next-copy>.small-note{font-size:11px;line-height:1.8;color:#697363;max-width:370px}.footer{min-height:125px;display:flex;align-items:center;justify-content:space-between;gap:20px}.footer .wordmark{font-size:22px}.footer p{font-family:var(--serif);font-style:italic;font-size:16px;color:var(--muted)}.footer>a:last-child{font-size:12px}.footer>a:last-child span{margin-left:14px}
@media(min-width:1600px){.hero{padding-block:110px}.wrap{width:min(1280px,calc(100% - 140px))}}
@media(max-width:900px){.wrap{width:calc(100% - 56px)}.hero{gap:25px;padding-block:65px}h1{letter-spacing:-2px}.intro{font-size:15px}.lesson{gap:35px;grid-template-columns:.85fr 1.15fr}h3{font-size:31px}.lesson-copy>p{font-size:14px}h2{font-size:36px}.next-inner{gap:40px}.next h2{font-size:38px}}
@media(max-width:640px){.wrap{width:calc(100% - 40px)}.navigation{height:84px}.wordmark{font-size:23px}.navigation nav{gap:19px;font-size:12px}.hero{grid-template-columns:1fr;padding-top:49px;padding-bottom:40px;gap:38px}h1{font-size:53px}.intro{font-size:16px;max-width:100%}.eyebrow{font-size:10px;letter-spacing:1.3px}.illustration{max-width:450px;width:100%;margin:auto;transform:none}.section-heading{display:block;padding-top:29px;padding-bottom:29px}.section-heading>p{margin-top:20px}.section-heading>p br{display:none}h2{font-size:34px}.lesson{grid-template-columns:1fr;gap:26px;padding:32px 0 37px}h3{font-size:34px;margin-top:16px}.lesson-copy>p{max-width:100%;font-size:15px}.topic-tags{margin:17px 0 0}.lesson-copy>.lesson-detail{display:none}.player figcaption{font-size:8px}.player figcaption>span:last-child{font-size:10px}.lessons{padding-bottom:15px}.next{padding:43px 0}.next-inner{grid-template-columns:1fr;gap:28px}.next h2{font-size:37px}.footer{padding-block:28px;min-height:120px;flex-wrap:wrap;gap:15px}.footer p{font-size:14px;margin:0}.footer>a:last-child{width:100%;margin-top:5px}}
@media(prefers-reduced-motion:reduce){html{scroll-behavior:auto}*{transition:none!important}}

/* Parent-facing preview additions and two accessible colour themes. */
:root{color-scheme:light}body{font-size:17px}.intro{font-size:18px}.navigation{height:auto;min-height:110px;gap:22px}.navigation nav{gap:25px;align-items:center;flex-wrap:wrap}.navigation nav a{font-size:15px}.theme-toggle,.text-button{font:inherit;cursor:pointer;border:1px solid var(--line);background:transparent;color:var(--ink);border-radius:4px;padding:10px 14px}.theme-toggle{font-size:14px;white-space:nowrap}button:focus-visible,input:focus-visible,textarea:focus-visible,select:focus-visible,summary:focus-visible{outline:3px solid var(--blue);outline-offset:4px}button:disabled{opacity:.5;cursor:not-allowed}.support-section{padding-block:25px 60px}.approach-grid{display:grid;grid-template-columns:repeat(3,1fr);gap:45px}.approach-grid h3{font-size:28px}.approach-grid p,.support-note{font-size:17px;line-height:1.8;color:var(--muted)}.step{font-family:var(--serif);color:var(--blue)}.support-note{border-top:1px solid var(--line);padding-top:25px;margin-top:35px;max-width:950px}.practice-panel{display:grid;grid-template-columns:1.3fr 1fr;border:1px solid var(--line);border-radius:5px;overflow:hidden}.practice-panel>div{padding:35px}.practice-panel p{line-height:1.8}.question-count{font-size:12px;letter-spacing:1.3px;color:var(--blue)}.practice-panel h3{font-size:30px}.practice-aside{background:var(--surface);border-left:1px solid var(--line)}.practice-aside p{color:var(--muted)}.practice-aside a,.contact-section a,.legal a,.small-note a{color:var(--blue);text-decoration:underline;text-underline-offset:3px}.answer-row{display:flex;gap:12px;margin-top:9px}.answer-row input{width:120px}.practice-actions{display:flex;flex-wrap:wrap;gap:15px;margin-top:18px}.text-button{font-size:14px}.practice-aside .small-note,.small-note{font-size:14px;line-height:1.8;color:var(--muted)}#solution{border-left:3px solid var(--blue);padding-left:20px;margin-top:25px}#solution p{font-family:var(--serif);font-size:23px;margin:8px 0}#answer-status[data-correct=true]{color:var(--blue)}.faq h2{margin-bottom:30px}.faq details{border-top:1px solid var(--line);padding:22px 0}.faq details:last-child{border-bottom:1px solid var(--line)}summary{font-size:18px;cursor:pointer;font-weight:550;padding-right:10px}.faq details p{max-width:850px;color:var(--muted);line-height:1.8;margin:18px 0 0}.contact-section{display:grid;grid-template-columns:1fr 1.25fr;gap:90px;padding-block:70px}.contact-section>div>p:not(.eyebrow){font-size:17px;line-height:1.8;max-width:350px}.contact-section .small-note{font-size:14px!important}.contact-form{border:1px solid var(--line);border-radius:5px;padding:30px}label{display:block;font-size:15px;font-weight:550;margin:17px 0 8px}input,textarea,select{font:inherit;font-size:16px;color:var(--ink);background:var(--paper);border:1px solid var(--input-line);border-radius:4px;padding:12px;width:100%;line-height:1.5}textarea{resize:vertical}.form-columns{display:grid;grid-template-columns:1fr 1fr;gap:18px}.optional{font-weight:400;color:var(--muted)}.preview-notice{background:var(--surface);border-left:3px solid var(--blue);padding:14px;font-size:14px;line-height:1.7;margin:0 0 20px}.spam-trap{position:absolute;left:-10000px;width:1px;height:1px;overflow:hidden}.footer{border-top:1px solid var(--line)}.footer nav{display:flex;gap:22px;flex-wrap:wrap;font-size:14px}.footer p{font-size:15px}.legal{max-width:850px;padding-block:55px}.legal h1{font-size:52px}.legal h2{font-size:29px;margin-top:35px}.legal p,.legal li{font-size:17px;line-height:1.9;color:var(--muted)}:root{--surface:#e9ede3;--input-line:#87958b}.next{background:var(--surface)}
[data-theme=dark]{color-scheme:dark;--paper:#141c20;--ink:#edf0e8;--muted:#b7c2bc;--line:#3c4948;--blue:#95b7ff;--surface:#202e32;--input-line:#82938e}.primary{background:var(--ink);color:var(--paper)}.primary:hover{background:var(--blue)}[data-theme=dark] .next{border-color:var(--line)}[data-theme=dark] .next-copy>p,[data-theme=dark] .next-copy>.small-note,[data-theme=dark] .topic-tags span,[data-theme=dark] .lesson-copy>.lesson-detail{color:var(--muted)}[data-theme=dark] .next li{border-color:var(--line)}[data-theme=dark] .next li span{color:var(--muted)}[data-theme=dark] .illustration svg text{fill:var(--muted)}[data-theme=dark] .illustration svg>text{fill:var(--blue)}[data-theme=dark] .illustration svg>path:nth-of-type(3){stroke:var(--blue)}[data-theme=dark] .illustration circle:last-of-type{fill:var(--blue)}[data-theme=dark] .illustration pattern path{stroke:#405054}[data-theme=dark] .figure-top,[data-theme=dark] .figure-bottom{border-color:var(--line)}
@media(max-width:1000px){.navigation{padding-block:22px}.navigation nav{gap:16px}.contact-section{gap:35px}.footer{padding-block:25px;flex-wrap:wrap}.footer nav{width:100%}.hero{grid-template-columns:1.2fr 1fr;gap:20px}h1{font-size:53px}}
@media(max-width:640px){.navigation{display:block;padding-block:22px}.navigation nav{margin-top:22px;justify-content:space-between;gap:8px}.navigation nav a{font-size:13px}.theme-toggle{font-size:12px;padding:9px}.hero{grid-template-columns:1fr}h1{font-size:46px;letter-spacing:-1.8px}.intro{font-size:17px}.approach-grid,.practice-panel,.contact-section{grid-template-columns:1fr}.approach-grid{gap:12px}.approach-grid h3{margin-top:12px}.practice-panel>div{padding:24px}.practice-aside{border-left:0;border-top:1px solid var(--line)}.contact-section{gap:25px;padding-block:45px}.contact-form{padding:22px}.form-columns{grid-template-columns:1fr;gap:0}.answer-row{flex-wrap:wrap}.answer-row input{flex:1;min-width:90px}.practice-actions{gap:10px}.practice-actions button{font-size:13px}.support-section{padding-bottom:40px}.footer nav{gap:16px}.legal h1{font-size:40px}h2{font-size:32px}}

/* Motion and interaction polish: no scroll interception or replacement cursor. */
html{scroll-padding-top:135px}.navigation{position:sticky;top:0;z-index:10;background:var(--paper);transition:box-shadow .25s,border-color .25s}.navigation.is-scrolled{box-shadow:0 8px 20px -18px var(--ink)}.navigation nav a{position:relative;padding-block:9px}.navigation nav a::after{content:"";position:absolute;left:0;right:0;bottom:2px;height:1px;background:var(--blue);transform:scaleX(0);transform-origin:left;transition:transform .22s ease}.navigation nav a:hover::after,.navigation nav a[aria-current]::after{transform:scaleX(1)}.navigation nav a[aria-current]{color:var(--blue)}.primary{transition:background .2s,box-shadow .2s,transform .2s}.primary:hover{transform:translateY(-2px);box-shadow:0 5px 12px #14232015}.primary:active{transform:translateY(0)}.primary span{transition:transform .22s}.primary:hover span{transform:translate(2px,-2px)}.theme-toggle,.text-button{transition:background .2s,border-color .2s}.theme-toggle:hover,.text-button:hover:not(:disabled){background:var(--surface);border-color:var(--muted)}.player video{transition:box-shadow .25s}.player:focus-within video{box-shadow:0 0 0 3px var(--blue)}.player figcaption{font-size:11px;letter-spacing:.7px}.graph-replay{font:inherit;font-family:var(--sans);font-size:12px;color:var(--muted);border:1px solid var(--line);border-radius:4px;background:var(--paper);padding:7px 10px;cursor:pointer;white-space:nowrap;margin-left:16px}.graph-replay:hover{color:var(--blue);border-color:var(--blue)}.graph-replay span{font-size:17px;margin-left:5px}.illustration{overflow:hidden}.illustration .figure-caption{font-size:15px}.faq summary::marker{color:var(--blue)}.faq details[open]{padding-bottom:26px}.lesson{padding-block:52px}.lesson-copy>.topic-tags{margin-bottom:0}.footer a:hover{text-decoration:underline;text-underline-offset:4px}
@media(max-width:640px){html{scroll-padding-top:25px}.navigation{position:relative}.lesson{padding-block:34px}.player figcaption{font-size:9px}.illustration .figure-caption{font-size:13px}.graph-replay{font-size:11px}.figure-bottom{gap:10px}}
@media(prefers-reduced-motion:reduce){html{scroll-behavior:auto}*,*::before,*::after{animation:none!important;transition:none!important}.primary:hover,.primary:hover span{transform:none}}

/* Darker paragraph text on the light paper background. */
[data-theme=light] .next-copy>p,[data-theme=light] .next-copy>.small-note,[data-theme=light] .small-note,[data-theme=light] .optional,[data-theme=light] .topic-tags span{color:var(--muted)}
[data-theme=light] .next li span{color:#536159}
[data-theme=light] input::placeholder,[data-theme=light] textarea::placeholder{color:#58645d;opacity:1}

/* Answer feedback uses words as well as accessible theme-specific colours. */
#answer-status{font-weight:600}#answer-status[data-correct=true]{color:#14703a}#answer-status[data-correct=false]{color:#b52c2c}[data-theme=dark] #answer-status[data-correct=true]{color:#7ee2a1}[data-theme=dark] #answer-status[data-correct=false]{color:#ff9696}

/* Final type scale: readable body copy, consistent controls and clear feedback. */
button,input,textarea,select{font-family:var(--sans)}
.primary{font-family:var(--sans);font-size:15px;font-weight:550;line-height:1.45;border:0;cursor:pointer}
.eyebrow{font-size:12px;letter-spacing:1.2px;line-height:1.6}
.hero-note,.question-count,.lesson-number span,.next .eyebrow{font-size:13px;line-height:1.6}
.lesson-copy>p,.section-heading>p,.next-copy>p,.approach-grid p,.practice-aside>p{font-size:17px;line-height:1.8}
.topic-tags span,.next li,.footer nav,.figure-top,.player figcaption,.player figcaption>span:last-child{font-size:13px;line-height:1.6}
.figure-top{font-size:12px;letter-spacing:.7px;gap:20px}.figure-top span:last-child{white-space:nowrap}
.next-copy>.small-note,.practice-aside .small-note,.small-note,.contact-section .small-note{font-size:14px!important;line-height:1.8}
.text-button,.graph-replay,.theme-toggle{font-size:14px;line-height:1.5}
#answer-status{font-family:var(--sans);font-size:18px;font-weight:650;line-height:1.6;min-height:2.9em;margin-block:16px 8px}
#contact-status{font-size:16px;line-height:1.7}
.practice-panel label,.contact-form label{font-size:16px}
.footer p{font-family:var(--sans);font-style:normal;font-size:15px}
@media(max-width:640px){.navigation nav a,.theme-toggle{font-size:13px}.lesson-copy>p,.section-heading>p,.next-copy>p,.approach-grid p,.practice-aside>p{font-size:16px}.figure-top{font-size:11px;letter-spacing:.4px;gap:12px}.player figcaption,.player figcaption>span:last-child{font-size:12px}.player figcaption{flex-wrap:wrap;gap:5px}.graph-replay,.text-button{font-size:14px}.figure-bottom{align-items:flex-start}#answer-status{font-size:18px}.eyebrow{font-size:12px}}

/* Planned features carry the same reading size as other body text. */
.next li{font-size:16px;line-height:1.7}