:root{--ink:#29433e;--green:#36786c;--deep:#205f56;--muted:#60746a;--line:#d3e0d7;--paper:#fffefa;--serif:'Yu Mincho','Hiragino Mincho ProN','Noto Serif CJK JP',serif;font:16px/1.75 'Yu Gothic','Hiragino Kaku Gothic ProN','Noto Sans CJK JP',sans-serif;color-scheme:light}
*{box-sizing:border-box}body{margin:0;color:var(--ink);background:radial-gradient(ellipse at 12% 0,#fffbed,transparent 55%),#f1f6f2}a{color:inherit;text-decoration:none}button,input,textarea{font:inherit;color:inherit}button,a,summary{touch-action:manipulation}button{cursor:pointer}button:disabled{opacity:.5;cursor:default}h1,h2,p{margin:0}b,strong{font-weight:600}button:focus-visible,a:focus-visible,input:focus-visible,textarea:focus-visible,summary:focus-visible{outline:3px solid #b5933d;outline-offset:3px}.shell{width:min(1120px,calc(100% - 36px));margin:auto}.top-nav{display:flex;justify-content:center;gap:10px;padding:13px 0}.top-nav a{border:1px solid #b3c9bb;border-radius:10px;background:#ffffffce;min-height:41px;padding:5px 15px;display:flex;align-items:center;gap:8px;font-size:.875rem}.top-nav svg{width:18px;height:18px;fill:none;stroke:currentColor;stroke-width:1.6;stroke-linecap:round;stroke-linejoin:round}.brand{text-align:center;color:var(--muted);font-size:.8125rem;letter-spacing:.035em}.intro{text-align:center;padding:25px 0 10px}.kicker{font-size:.875rem;letter-spacing:.1em;color:#7c7d51}.intro h1{font:500 2.5rem/1.5 var(--serif);margin-top:5px;letter-spacing:.1em}.subtitle{font:500 1.2rem/1.8 var(--serif);margin-top:4px}.intro-note{color:var(--muted);margin-top:13px;line-height:1.9}.download-row{display:flex;justify-content:center;gap:10px;flex-wrap:wrap;margin-top:21px}.button{display:inline-flex;align-items:center;justify-content:center;gap:9px;min-height:44px;padding:8px 15px;border-radius:9px;border:1px solid #a9c3b2;background:white;font-size:.9375rem;line-height:1.6}.button:hover:not(:disabled){background:#edf5ec}.button.primary{color:white;background:var(--green);border-color:var(--green)}.button.primary:hover{background:var(--deep)}.button.gold{color:#826321;background:#fff7de;border-color:#dcc99c}.button small{font-size:.8125rem;opacity:.85}.pdf-note{font-size:.8125rem;color:var(--muted);margin-top:10px}.progress{max-width:390px;margin:20px auto 0;font-size:.875rem}.progress span{display:flex;justify-content:space-between}.progress progress{display:block;width:100%;height:7px;margin-top:8px;accent-color:var(--green);border:0;border-radius:9px;overflow:hidden}.progress progress::-webkit-progress-bar{background:#dce6dc}.progress progress::-webkit-progress-value{background:#6e9b7f}.level-section{margin:25px 0 30px}.section-head{display:flex;justify-content:space-between;align-items:baseline;gap:10px;border-bottom:1px solid #bdd1c2;padding-bottom:10px;margin-bottom:12px}.section-head h2{font:500 1.25rem/1.6 var(--serif)}.section-head h2 small{font:.875rem 'Yu Gothic',sans-serif;margin-left:15px;color:var(--muted)}.section-head p{font-size:.875rem;color:var(--muted)}.cards{display:grid;grid-template-columns:1fr 1fr;gap:11px}.card{display:grid;grid-template-columns:40px 1fr 15px;gap:12px;align-items:center;padding:15px 18px;border:1px solid var(--line);border-radius:13px;background:var(--paper);box-shadow:0 5px 20px #244c3505;min-height:96px}.card:hover{border-color:#7ba48b;background:#fffffc}.card-number{font:1.7rem Georgia,serif;color:#7b9d86}.card b{font:500 1.12rem/1.7 var(--serif)}.card small{display:block;font-size:.8125rem;color:var(--muted);margin-top:4px}.chevron{font-size:1.4rem;color:#718575}.lesson-heading{padding-top:16px}.title-row{display:flex;justify-content:center;align-items:center;gap:12px;flex-wrap:wrap}.title-row h1{font:500 clamp(1.3rem,2.4vw,1.8rem)/1.6 var(--serif)}.number{font:2rem Georgia,serif;color:#789f87}.level{font-size:.875rem;color:#85672d;border:1px solid #decda4;background:#fff8e4;border-radius:18px;padding:1px 11px}.question-nav{display:flex;justify-content:center;gap:6px;flex-wrap:wrap;margin:14px auto 20px}.question-nav a{width:39px;min-height:36px;display:grid;place-items:center;position:relative;background:#ffffffbc;border:1px solid var(--line);border-radius:8px;font-size:.875rem}.question-nav a[aria-current]{background:var(--green);color:white;border-color:var(--green)}.question-nav .done:after{content:'✓';position:absolute;top:-8px;right:-5px;border-radius:50%;background:#f6ebc6;color:#81662a;font-size:.75rem;width:16px;height:17px;line-height:17px;text-align:center}.practice-layout{display:grid;grid-template-columns:minmax(0,1.3fr) minmax(330px,1fr);gap:16px;align-items:start}.paper,.answer-panel{background:var(--paper);border:1px solid var(--line);border-radius:17px;padding:23px;box-shadow:0 8px 25px #2f4e3b05;min-width:0}.eyebrow{font-size:.875rem;letter-spacing:.08em;color:var(--green);margin-bottom:13px}.problem,.ask{font-size:1.0625rem;line-height:2}.ask{border-left:3px solid #a4b797;margin:16px 0 23px;padding-left:12px;font-weight:600}.notes-head{display:flex;justify-content:space-between;align-items:baseline;gap:8px;flex-wrap:wrap}.notes-head label{font-size:1rem}.notes-head span{font-size:.8125rem;color:var(--muted)}textarea{display:block;width:100%;min-height:232px;resize:vertical;border:1px solid #bbccbe;border-radius:9px;padding:13px;background:#fff;line-height:1.9;font-size:1rem;margin-top:9px}textarea::placeholder{font-size:.875rem;color:#819084}.study-note{font-size:.875rem;color:var(--muted);margin-top:9px}.answer-panel h2{font-size:1.05rem;font-weight:500;margin-bottom:14px}.answer-item{margin:10px 0}.answer-item label{display:block;font-size:.9375rem;margin-bottom:4px}.answer-box{display:flex;align-items:center;gap:8px}.answer-box input{width:112px;min-height:45px;background:white;border:1px solid #a2bea9;border-radius:8px;text-align:center;font-size:1.3rem}.answer-box input[aria-invalid=true]{border-color:#bc9a4c;background:#fff9e8}.field-mark{color:var(--green);font-size:1.15rem}.check{width:100%;margin-top:10px}.feedback{margin-top:10px;font-size:.9375rem;color:#896928;line-height:1.8}.feedback:empty{display:none}.feedback.good{color:var(--green)}.hint-wrap{border-top:1px solid var(--line);padding-top:14px;margin-top:16px}.hint-top{display:flex;justify-content:space-between;align-items:center;gap:10px}.hint-top>span{font-size:.875rem;color:var(--muted)}.hint{background:#fff7e1;border:1px solid #e5d4a6;border-radius:9px;padding:10px 12px;margin-top:10px;font-size:.9375rem;line-height:1.85}.hint b{display:block;font-size:.8125rem;color:#927030;margin-bottom:3px}.solution{margin-top:15px;border-top:1px solid var(--line)}.solution summary{cursor:pointer;font-size:.9375rem;color:var(--deep);padding:11px 0}.solution ol{padding-left:23px;margin:2px 0 15px}.solution li{font-size:.875rem;margin-top:12px;line-height:1.8}.solution strong{display:block;color:var(--deep);font-size:1.05rem;font-weight:500;overflow-wrap:anywhere}.key{font-size:.9375rem;background:#f5f0db;border-left:3px solid #b7a266;padding:10px 12px;line-height:1.85}.final-answer{background:#e9f1e7;border-radius:9px;margin-top:12px;padding:10px 12px;font-size:.9375rem}.retry{background:none;border:0;text-decoration:underline;text-underline-offset:4px;color:var(--muted);font-size:.8125rem;padding:12px 0 0}.next-row{display:flex;justify-content:space-between;gap:12px;border-top:1px solid var(--line);margin-top:17px;padding-top:12px;font-size:.875rem}.award{display:flex;gap:12px;align-items:center;border:1px solid #d5c591;background:linear-gradient(120deg,#fbf1d76b,#edf3e43d);padding:10px 12px;border-radius:11px;margin-top:13px;min-height:117px}.gold-medal{width:88px;height:101px;opacity:.8;flex-shrink:0}.award small{font-size:.8125rem;letter-spacing:.07em;color:#95752c}.award b{display:block;font:500 1.55rem/1.7 var(--serif);color:#8e6b24}.award p{font-size:.875rem;color:var(--muted);line-height:1.7}footer{text-align:center;color:var(--muted);font-size:.8125rem;padding:24px 0}
@media(prefers-reduced-motion:no-preference){.button,.card{transition:background .15s,border-color .15s}.award.animate .gold-medal{animation:medal .7s ease-out}@keyframes medal{0%{opacity:0;transform:scale(.4) rotate(-14deg)}65%{transform:scale(1.1) rotate(3deg)}100%{opacity:.8;transform:scale(1) rotate(0)}}}
@media(max-width:800px){.shell{width:min(650px,calc(100% - 24px))}.practice-layout{display:flex;flex-direction:column;gap:12px}.paper,.answer-panel{width:100%;padding:20px}.question-nav{max-width:360px;gap:7px}.question-nav a{width:40px}.cards{grid-template-columns:1fr}.section-head{align-items:flex-start}.section-head p{max-width:55%;text-align:right}.paper textarea{min-height:160px}.answer-item{display:flex;align-items:center;justify-content:space-between;gap:10px}.answer-item label{margin:0}.answer-box{flex-shrink:0}}
@media(max-width:480px){.shell{width:calc(100% - 18px)}.top-nav{gap:7px;padding:10px 0}.top-nav a{padding:5px 11px;font-size:.875rem}.brand{font-size:.75rem;letter-spacing:0}.intro{padding-top:20px}.intro h1{font-size:2.1rem}.subtitle{font-size:1.13rem}.intro-note{font-size:.9375rem}.download-row{gap:8px}.download-row .button{width:100%;max-width:330px;justify-content:space-between}.pdf-note{font-size:.8125rem}.progress{margin-left:8px;margin-right:8px}.card{padding:13px;min-height:87px;gap:8px}.card b{font-size:1.06rem}.section-head p{font-size:.8125rem}.section-head h2 small{margin-left:10px}.title-row{gap:8px}.title-row h1{font-size:1.2rem}.number{font-size:1.7rem}.level{font-size:.8125rem;padding:1px 8px}.question-nav{max-width:325px;gap:6px;margin-bottom:15px}.question-nav a{width:38px;min-height:35px}.paper,.answer-panel{padding:16px}.problem,.ask{font-size:1rem;line-height:1.9}.ask{margin:13px 0 18px}.notes-head span{font-size:.8125rem}.answer-item{flex-wrap:wrap}.answer-box{margin-left:auto}.answer-box input{width:96px}.field-mark{width:14px}.award{gap:9px;padding:10px}.gold-medal{width:80px;height:92px}.award b{font-size:1.45rem}.gold-medal+div{min-width:0}.retry{font-size:.875rem}}

.related{border-top:1px solid var(--line,#d6e3dc);padding-top:16px;margin-top:20px;font-size:14px}.related a{display:block;color:#286456;text-decoration:underline;text-underline-offset:3px;padding:9px 0}.related small{display:block;color:#61766d;font-size:13px}.top-nav{flex-wrap:wrap}.top-nav a{min-height:44px}h1:focus{outline:none}

.question-figure{margin:14px 0 4px;padding:10px 4px;background:#f3f7f1;border:1px solid #d3e0d7;border-radius:10px}.question-figure svg{width:100%;height:auto;display:block}.question-figure text{font-family:'Yu Gothic','Hiragino Kaku Gothic ProN','Noto Sans CJK JP',sans-serif}.answer-box select{font:inherit;font-size:1.0625rem;border:1px solid #a2bea9;min-height:45px;border-radius:8px;background:white;padding:5px 12px}.answer-box select[aria-invalid=true]{border-color:#bc9a4c;background:#fff9e8}.answer-box select:focus-visible{outline:3px solid #b5933d;outline-offset:3px}.paper textarea{min-height:185px}.question-nav{max-width:670px;margin-left:auto;margin-right:auto}[hidden]{display:none!important}.skip-link{position:absolute;left:12px;top:-60px;background:#fff;padding:8px 12px;z-index:2}.skip-link:focus{top:8px}@media(max-width:480px){.question-figure{padding:7px 1px}.question-figure text{font-size:18px}.question-nav{max-width:325px}.section-head{display:block}.section-head p{max-width:none;text-align:left;margin-top:3px}}

.progress-detail{font-size:.8125rem;text-align:left;color:var(--muted);margin-top:8px}.resume-link{display:inline-block;max-width:100%;padding:8px 13px;margin-top:15px;border:1px solid #c2d2c5;border-radius:8px;background:#fffefa;font-size:.875rem;overflow-wrap:anywhere}.card.reviewed{border-left:3px solid #c4ad72}.card.done{border-left:3px solid #78a18a}.question-nav .reviewed:after{content:'・';position:absolute;top:-8px;right:-5px;background:#f6ebc6;color:#81662a;border-radius:50%;width:16px;height:17px;line-height:14px;text-align:center}.question-nav .started{border-bottom:3px solid #a9bcae}.solution-bridge{font-size:.9375rem;line-height:1.85;margin:2px 0 12px}.solution-figure{margin:10px 0 14px;padding:9px 3px;border:1px solid #d4e1d4;border-radius:9px;background:#f5f8f2}.solution-figure svg{width:100%;height:auto;display:block}.solution-figure text{font-family:'Yu Gothic','Hiragino Kaku Gothic ProN',sans-serif}.reset-status{font-size:.8125rem;color:var(--muted);margin-top:8px;line-height:1.8}.reset-status:empty{display:none}.reset-status button{border:0;background:transparent;color:var(--green);text-decoration:underline;padding:4px 8px;min-height:34px}.answer-item label{overflow-wrap:anywhere}.answer-panel,.paper{scroll-margin-top:12px}@media(max-width:480px){.solution-figure text{font-size:20px}.solution-figure{overflow-x:auto}.solution-figure svg{min-width:380px}.progress-detail{font-size:.8125rem}.resume-link{font-size:.875rem}}

/* Chapter 17: calm mint diagrams and room for decimal answers. */
:root{--green:#427b6c;--deep:#2c6356;--paper:#fffefd;--line:#d5e2da}.question-figure{background:linear-gradient(135deg,#f2f7f2,#f8f9f3)}.question-figure text{font-family:'Noto Sans JP','Yu Gothic',sans-serif}.pi-note{font-size:.875rem;color:var(--muted);margin:-5px 0 12px}.answer-box input{width:124px}.question-figure figcaption{font-size:.8125rem;color:var(--muted);text-align:center}.question-nav{max-width:750px}@media(max-width:480px){.answer-box input{width:112px}.question-figure text{font-size:21px}.question-nav{max-width:325px}}

.top-nav .nav-icon{width:18px;height:18px;flex:0 0 18px;fill:none;stroke:currentColor;stroke-width:1.65;stroke-linecap:round;stroke-linejoin:round}
.top-nav a{display:inline-flex;align-items:center;justify-content:center;gap:8px;white-space:nowrap}
.solution-figure{margin:15px 0;padding:8px;border:1px solid #d5e2da;border-radius:10px;background:#f6faf7}.solution-figure svg{display:block;width:100%;height:auto}
.level-section:last-child .section-head h2{font-size:20px}@media(max-width:600px){.level-section:last-child .section-head{display:block}.level-section:last-child .section-head p{max-width:none;text-align:left}}
