/* Shared textbook typography for React and immutable-source static lessons. */
.reader-shell{--reader-ui:"Microsoft YaHei","PingFang SC",system-ui,sans-serif;--reader-book:var(--reader-ui);--reader-body-size:18px;--reader-ink:#183c40;--reader-line:#e2e4dc;background:#f4f4ef;color:#263432;font-family:var(--reader-ui);line-height:1.8}
.reader-shell[data-text-size=large]{--reader-body-size:20px}
.reader-shell .reader-main,.reader-static main.reader-main{max-width:1280px;padding:26px 40px 40px}
.reader-shell .reader-card{background:#fffefa;max-width:968px;padding:34px 44px;border-radius:6px;border:1px solid #e2e4dc;box-shadow:none;font-family:var(--reader-book);font-size:var(--reader-body-size);line-height:1.8}
.reader-shell .reader-heading h1{font-family:var(--reader-book);font-size:28px;font-weight:600;line-height:1.5;letter-spacing:0;margin-bottom:14px}
.reader-shell .reader-heading{padding-bottom:24px;margin-bottom:28px}.reader-shell :is(h2,h3,h4){font-family:var(--reader-book);font-weight:600;letter-spacing:0}.reader-shell h2{font-size:1.3em}.reader-shell h3{font-size:1.13em}.reader-shell h4{font-size:1.06em}
.reader-shell :is(button,summary,.reader-eyebrow,.reader-topics,.reader-resource-actions,.reader-source-note,figcaption,.reader-footer,.reader-toolbar,.reader-sidebar,.reader-mobile-bar,.reader-reading-tools){font-family:var(--reader-ui)}
.reader-shell .reader-sidebar{background:#15383c}.reader-shell .reader-course{font-weight:600}.reader-shell .reader-nav-item[aria-current=page]{background:#e2eeea;border-left:3px solid #93b9af}.reader-shell .reader-nav-item{border-left:3px solid transparent}
.reader-shell .reader-reading-tools{position:sticky;top:0;z-index:15;display:flex;justify-content:space-between;gap:12px;align-items:center;background:#f4f4eff5;backdrop-filter:blur(8px);padding:9px 0;margin:0 0 14px;border-bottom:1px solid #dce1d8;font-size:13px}
.reader-reading-tools nav,.reader-reading-tools [role=group]{display:flex;align-items:center;gap:4px}.reader-reading-tools button{border:0;background:transparent;color:#405d5d;padding:7px 12px;border-radius:4px;font-size:13px}.reader-reading-tools button:hover,.reader-reading-tools button[aria-pressed=true]{background:#e0eae3;color:#173f40}.reader-reading-tools [role=group]>span{margin-right:5px;color:#66746d}
.reader-shell [data-reader-section],.reader-static .question,.reader-static .solution,.reader-static .marks{scroll-margin-top:75px}
.reader-shell .reader-disclosure{border:0;border-top:1px solid #b7c9c2;border-radius:0;margin:26px 0;background:transparent}.reader-shell .reader-disclosure-toggle,.reader-static .reader-disclosure>summary{background:transparent;color:#234c4c;padding:15px 0;font-size:16px;line-height:1.6}.reader-shell .reader-disclosure-body,.reader-shell .reader-full-solution>.reader-disclosure-body{padding:4px 0 20px}
.reader-shell .reader-step-group{margin:24px 0}.reader-shell .reader-step-group>h3{font-size:1.06em;color:#365954;border-bottom:1px solid #e0e5dd;padding-bottom:9px}.reader-shell .reader-continuous-step{padding:20px 0;border-bottom:0}.reader-shell .reader-continuous-step h4{font-size:1.06em;margin:0 0 12px;font-weight:600;color:#234e4d}.reader-shell .reader-continuous-step h4>span:first-child{font-family:var(--reader-ui);font-size:13px;font-weight:600;color:#4c7471;letter-spacing:.03em}
.reader-shell .step-block{margin:10px 0}.reader-shell .step-block>small{font-family:var(--reader-ui);font-size:12px;font-weight:500;letter-spacing:.04em;color:#617871}.reader-shell .step-why{background:transparent;border-left:2px solid #b6cec1;border-radius:0;padding:4px 0 4px 18px;margin:18px 0}
.reader-shell .reader-strategy{background:#f1f4ed;border-left:2px solid #95b3a1;border-radius:0;padding:16px 22px;margin:28px 0;font-family:var(--reader-book);line-height:1.8}.reader-shell .reader-strategy h3{margin-top:0}.reader-shell .reader-answer{border-top:1px solid #b7c9c2;padding-top:14px}.reader-shell .step-inline-warning,.reader-shell .mistake{background:#f7f2e5;border-radius:3px;padding:12px 16px;color:#584d34}
.reader-shell .katex{font-size:1.08em}.reader-shell .katex-display{margin:1em 0}.reader-shell .math-block{background:transparent;border:0;padding:8px 0}.reader-shell .tag-list{gap:6px}.reader-shell .tag-list>span{font:500 12px/1.7 var(--reader-ui);border:0;border-radius:3px;background:#eff2eb;color:#4d655c;padding:4px 8px}
.reader-shell .mark-list>div{display:grid;grid-template-columns:48px minmax(0,1fr);gap:14px;margin:12px 0;align-items:start}.reader-shell .mark-list b{font:600 13px/1.8 var(--reader-ui);color:#315d58;background:#e9f0e9;border-radius:3px;padding:3px 6px;text-align:center}.reader-shell .mark-list p{margin-top:0}.reader-score-label{display:block;margin:28px 0 14px;font:600 15px/1.6 var(--reader-ui)}
.reader-ms-heading{display:flex;gap:12px;justify-content:space-between;align-items:center;font:500 13px/1.7 var(--reader-ui)}.reader-ms-heading a{font-size:12px}.reader-shell .reader-ms-gallery figure{margin:18px 0}.reader-ms-preview{position:relative;background:#fff;border:1px solid #dbe0d8;padding:10px}.reader-ms-preview>img{display:block;width:100%;height:auto}.reader-ms-preview>button{position:absolute;inset:0;width:100%;border:0;background:transparent;color:transparent;cursor:zoom-in}.reader-ms-preview>button:focus-visible{color:#193c3c;background:#ffffffbb}.reader-ms-gallery figcaption{font-size:12px;color:#677a72;margin-top:6px;text-align:center}.reader-image-error{display:block;position:relative;z-index:1;padding:24px;text-align:center;font:14px var(--reader-ui)}.reader-image-empty{font-size:14px}
.reader-image-backdrop{position:fixed;inset:0;z-index:100;background:#0f262ccc;display:grid;place-items:center;padding:24px}.reader-image-dialog{width:min(1120px,96vw);max-height:94vh;display:flex;flex-direction:column;background:#fffefa;border-radius:8px;overflow:hidden;font:14px/1.6 system-ui,sans-serif;color:#213e3b}.reader-image-dialog header,.reader-image-dialog nav{display:flex;align-items:center;gap:12px;padding:12px 18px;border-bottom:1px solid #e0e5de}.reader-image-dialog header strong{margin-right:auto}.reader-image-dialog button{font:inherit;padding:6px 10px;border:1px solid #bdcec7;background:#f7f9f4;border-radius:4px;color:#234d47}.reader-image-dialog button:focus-visible{outline:3px solid #a5792d}.reader-image-dialog button:disabled{opacity:.45}.reader-image-scroll{overflow:auto;padding:18px;min-height:0}.reader-image-scroll img{display:block;width:100%;max-width:none;height:auto}.reader-image-scroll img.is-zoomed{width:200%}
.reader-static .reader-card .solution-body{font-size:var(--reader-body-size);line-height:1.8}.reader-static .reader-card :is(.pre,.strategy,.transfer){background:transparent;border-radius:0}.reader-static .reader-card .strategy{background:#f1f4ed}.reader-static .reader-card .question{background:transparent;border:0;padding:0}.reader-static .reader-heading h1{font-size:28px}.reader-static .reader-card .solution-body>h3{font-size:1.12em}.reader-static .reader-card .solution-body :is(p,li){font-size:inherit}.reader-static .reader-card .mark-code{font-family:var(--reader-ui)}
@media(max-width:1100px){.reader-shell .reader-main,.reader-static main.reader-main{padding:22px}.reader-shell .reader-card{padding:28px}.reader-shell .reader-heading h1{font-size:25px}}
@media(max-width:760px){.reader-shell{--reader-body-size:17px}.reader-shell[data-text-size=large]{--reader-body-size:19px}.reader-shell .reader-main,.reader-static main.reader-main{padding:12px 10px 28px}.reader-shell .reader-card,.reader-static article.reader-card{padding:23px 18px;border-radius:4px}.reader-shell .reader-heading h1{font-size:23px}.reader-shell .reader-reading-tools{gap:4px;padding:7px 0}.reader-reading-tools button{padding:7px 8px;font-size:12px}.reader-reading-tools [role=group]>span{display:none}.reader-shell .reader-disclosure-toggle{font-size:15px!important;padding:14px 0}.reader-shell .reader-full-solution>.reader-disclosure-body{padding:0}.reader-shell .reader-strategy{padding:14px 16px}.reader-shell .reader-continuous-step{padding:17px 0}.reader-image-backdrop{padding:8px}.reader-image-dialog{width:100%;max-height:96vh}.reader-image-dialog header{flex-wrap:wrap}.reader-ms-heading{align-items:flex-start;flex-direction:column;gap:4px}.reader-shell .mark-list>div{grid-template-columns:42px minmax(0,1fr);gap:10px}}
@media print{.reader-reading-tools{display:none!important}.reader-shell .reader-card{border:0;background:white}.reader-shell{background:white}}

/* Reading controls belong to the page chrome, never to nested KaTeX nodes. */
.reader-shell .reader-reading-tools{position:static;justify-content:flex-end;background:transparent;border:0;margin:0 0 0 auto;padding:0}
.reader-shell .reader-full-solution>.reader-disclosure-toggle[aria-expanded=false],.reader-static .reader-full-solution:not([open])>summary{display:flex;align-items:center;justify-content:space-between;gap:20px;background:#1c5558;color:#fff;border:1px solid #1c5558;border-radius:7px;padding:15px 22px;font:600 16px/1.5 var(--reader-ui);cursor:pointer;min-height:52px}
.reader-shell .reader-full-solution>.reader-disclosure-toggle[aria-expanded=false]:hover,.reader-static .reader-full-solution:not([open])>summary:hover{background:#123e42}
.reader-shell .reader-full-solution>.reader-disclosure-toggle:focus-visible,.reader-static .reader-full-solution>summary:focus-visible{outline:3px solid #bc9559;outline-offset:4px}
.reader-static .reader-full-solution>summary::after{content:'⌄';margin-left:auto}.reader-static .reader-full-solution[open]>summary::after{content:'⌃'}
.reader-progress{position:fixed;right:max(16px,calc((100vw - 1540px)/2));top:40%;z-index:20;font:13px/1.5 var(--reader-ui);color:#45645f}
.reader-progress-panel{display:flex;gap:12px;align-items:stretch;padding:16px 12px;background:#f4f4eff5;border:1px solid #dde3d9;border-radius:10px}
.reader-progress nav{display:flex;flex-direction:column;justify-content:space-between;gap:25px}
.reader-progress nav button{border:0;background:transparent;padding:5px;color:#56716b;text-align:left;cursor:pointer;font:inherit}
.reader-progress nav button[aria-current=location]{color:#154d50;font-weight:700}.reader-progress button:focus-visible,.reader-progress-track:focus-visible{outline:3px solid #bc9559;outline-offset:3px}
.reader-progress-track{position:relative;width:18px;min-height:144px;cursor:ns-resize;touch-action:none;background:linear-gradient(#ced9d0,#ced9d0) center/2px 100% no-repeat;border-radius:8px}
.reader-progress-fill{position:absolute;left:8px;top:0;width:2px;background:#40746d;pointer-events:none}.reader-progress-thumb{position:absolute;left:3px;width:12px;height:12px;transform:translateY(-50%);background:#246266;border:2px solid #fffefa;border-radius:50%;box-shadow:0 0 0 1px #246266;pointer-events:none}
.reader-progress-trigger{display:none}.reader-step-marks{display:flex;flex-wrap:wrap;gap:8px;margin:14px 0 4px;font:13px/1.6 var(--reader-ui)}.reader-step-marks details{border:0}.reader-step-marks summary{display:inline-block;list-style:none;cursor:pointer;background:#e7eee7;border:1px solid #bdcfc5;border-radius:4px;padding:3px 9px;color:#285c56;font-weight:600}.reader-step-marks summary:focus-visible{outline:3px solid #bc9559}.reader-step-marks details[open]{flex-basis:100%}.reader-step-marks .reader-score-condition{padding:10px 0;color:#3b554e;font-size:14px}
@media(min-width:1024px){.reader-shell .reader-main,.reader-static main.reader-main{padding-right:138px}.reader-progress-panel{display:flex}}
@media(max-width:1023px){.reader-progress{right:10px;top:auto;bottom:26px}.reader-progress-trigger{display:block;border:1px solid #b3c9bf;background:#1c5558;color:white;border-radius:22px;padding:10px 14px;font:600 12px var(--reader-ui);box-shadow:0 3px 12px #15383c22}.reader-progress-panel{display:none;position:absolute;right:0;bottom:46px;min-width:115px;box-shadow:0 4px 24px #15383c19}.reader-progress.is-expanded .reader-progress-panel{display:flex}.reader-progress-track{display:none}.reader-progress nav{gap:8px}.reader-progress nav button{min-height:40px}.reader-shell .reader-full-solution>.reader-disclosure-toggle[aria-expanded=false],.reader-static .reader-full-solution:not([open])>summary{padding:15px 18px!important}}
/* Keep the compact trigger in the page margin, clear of derivations. */
@media(max-width:760px){.reader-progress{right:0;top:50%;bottom:auto;transform:translateY(-50%)}.reader-progress-trigger{box-sizing:border-box;width:26px;min-height:88px;padding:10px 4px;border-radius:9px 0 0 9px;writing-mode:vertical-rl;letter-spacing:.1em}.reader-progress-trigger:focus-visible{outline-offset:-3px}.reader-progress-panel{right:30px;top:0;bottom:auto;transform:translateY(-25%)}}
@media print{.reader-progress{display:none}}

/* V5: reviewed mathematical blocks preserve their authored order. */
.reader-authored-flow p{margin:10px 0;line-height:1.8}.reader-derivation{margin:12px 0;min-width:0}.reader-derivation .math-display{display:block}.reader-shell .reader-derivation .katex-display{margin:.65em 0}.reader-continuous-step:has(.reader-authored-flow){padding:14px 0}.reader-authored-flow .teaching-visual{margin:18px 0}
@media(max-width:760px){.reader-derivation .katex-display>.katex{text-align:left}.reader-shell .reader-derivation .katex-display{margin:.55em 0}}
.reader-score-route-note{font:14px/1.7 var(--reader-ui);color:#4c6966;margin:12px 0 20px}.reader-score-route+.reader-score-route{border-top:1px solid #e0e5dd;margin-top:24px;padding-top:16px}.reader-score-route h4{font:600 15px/1.7 var(--reader-ui);color:#365954;margin:8px 0 14px}
.reader-shell .math-inline{padding-inline:.18em}