@charset "UTF-8";
/* Source callouts and wide figures retain readable space on a phone. */
.prose img{max-width:100%;height:auto}
.prose blockquote{margin:20px 0;padding:15px 16px;background:var(--light);border-left:3px solid var(--teal);border-radius:0 10px 10px 0}
.prose figure{margin:20px 0;max-width:100%;overflow-x:auto}
.prose figure img{display:block;max-width:none;height:auto}
.prose figcaption{font:12px/1.6 -apple-system,BlinkMacSystemFont,"Segoe UI",Arial,sans-serif;color:var(--muted);margin-top:10px}
.katex-display>.katex{width:max-content;min-width:100%}
.skip{transform:translateY(-150%)}.skip:focus{transform:translateY(0)}
:root{--paper:#f7f5ef;--card:#fffefa;--ink:#173440;--muted:#6b7879;--line:#e3e5dd;--teal:#226c68;--light:#eaf2ec;--gold:#e8c680;--navy:#102f3d;--danger:#a23f38;--body-size:17px;font-family:Inter,-apple-system,BlinkMacSystemFont,"Segoe UI",Arial,sans-serif;color:var(--ink);background:var(--paper);font-synthesis:none;line-height:1.5}
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var(--line);padding:9px 14px;background:var(--card);color:var(--muted);font-size:12px}.saved-tabs button.active{background:var(--light);color:var(--teal);border-color:#a7c3ad}#toast{position:fixed;bottom:25px;left:calc(50% + 125px);transform:translateX(-50%);background:var(--navy);color:#fff;padding:12px 19px;border-radius:10px;z-index:80;font-size:12px;box-shadow:0 4px 15px #0002;max-width:85%;display:none}#toast.visible{display:block}.mono{font-family:ui-monospace,SFMono-Regular,monospace;font-size:11px}.section-toc-mobile{display:none}
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@media(min-width:1450px){main{padding-top:48px}.hero-grid{gap:30px}.book-card{min-height:420px}.chapter-preview,.daily-list{gap:20px}}
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/* Isbot: book library and official institute credit. */
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/* Preserve source geometry while making small diagram labels readable. */
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/* Six volumes form two balanced shelf rows on a wide screen. */
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/* Book-based multiple-choice practice. */
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@media(max-width:1100px){.quiz-layout{grid-template-columns:minmax(0,1fr) 205px}.quiz-map{padding:20px 16px}}
@media(max-width:850px){.bottom-nav{grid-template-columns:repeat(6,minmax(0,1fr))}.bottom-nav a small{font-size:8px}.quiz-layout{grid-template-columns:minmax(0,1fr)}.quiz-map{padding:23px}.quiz-grid{grid-template-columns:repeat(10,minmax(0,1fr))}.quiz-map>.btn{width:auto}.quiz-home-card{padding:23px}.quiz-home-card h2{font-size:23px}}
@media(max-width:620px){.quiz-home-card{align-items:start;flex-direction:column;gap:20px}.quiz-home-card .btn{width:100%}.quiz-hero{grid-template-columns:minmax(0,1fr);gap:25px;padding:23px}.quiz-hero h2{font-size:30px}.quiz-hero .button-row .btn{width:100%}.quiz-stat{border-left:0;border-top:1px solid var(--line);padding:22px 0 0;grid-template-columns:1fr 1fr;text-align:left;align-items:center}.quiz-stat b{grid-row:1/3;font-size:31px}.quiz-stat span,.quiz-stat small{text-align:right}.quiz-question{padding:22px 18px}.quiz-question legend .prose{font-size:19px}.quiz-option{padding:14px 11px;gap:9px}.quiz-option .prose{font-size:17px}.quiz-status{align-items:start;flex-direction:column;gap:5px}.quiz-topline{gap:8px;align-items:start}.quiz-topline>span{font-size:10px;text-align:right;margin-top:10px}.quiz-grid{grid-template-columns:repeat(5,minmax(0,1fr));gap:9px}.quiz-number{height:40px;font-size:13px}.quiz-result{padding:24px;gap:25px}.quiz-result>.btn{width:100%}.quiz-result-counts{gap:17px}.quiz-score strong{font-size:49px}.quiz-score strong small{font-size:14px}.quiz-review>summary{padding:15px 13px;gap:9px}.quiz-review>summary>span:nth-child(2){font-size:11px}.quiz-review-body{padding:7px 17px 23px}.quiz-history-row{padding:17px 15px}.quiz-history-row>b{font-size:17px}.quiz-history-row strong{font-size:12px}.quiz-history-row small{font-size:10px}.quiz-history-row>b span{margin-left:4px}.quiz-question-actions{gap:3px}.quiz-confirm .button-row>.btn{width:100%}}

/* Selected official Isbot app mark. */
.brand .brand-logo{width:48px;height:48px;object-fit:contain;border-radius:12px;flex-shrink:0;background:#131210}
.mobile-logo{width:38px;height:38px;object-fit:contain;border-radius:10px;flex-shrink:0}
@media(max-width:360px){.mobile-brand b{font-size:21px}.mobile-logo{width:32px;height:32px}.header-institute{gap:7px;max-width:190px}.header-institute img{width:36px;height:36px}.header-institute b{font-size:10px}}

/* Long inline formulas stay within a narrow test card. */
.quiz-question .prose,.quiz-review .prose,.quiz-review-options li>span{max-width:100%;overflow-x:auto;overflow-y:hidden}
.quiz-review>summary>span:nth-child(2){min-width:0;overflow-wrap:anywhere}

/* Saved configuration applies only to the next attempt. */
.quiz-config{display:grid;grid-template-columns:minmax(0,1fr) 150px;gap:20px;align-items:start;margin:22px 0}.quiz-book-choices{min-width:0;border:0;padding:0;margin:0}.quiz-book-choices legend,.quiz-count-choice>span{display:block;font-size:12px;font-weight:700;color:var(--ink);margin:0 0 10px}.quiz-book-choice{display:flex;align-items:center;gap:12px;padding:12px;border:1px solid var(--line);border-radius:10px;margin-bottom:9px;background:var(--card);cursor:pointer}.quiz-book-choice input{margin:0}.quiz-book-choice strong{display:block;font-size:12px;line-height:1.6;font-weight:600}.quiz-book-choice small{display:block;color:var(--muted);font-size:10px;margin-top:3px}.quiz-count-choice select{width:100%;font-size:13px}.quiz-hero p.quiz-selection-summary{font-size:12px;color:var(--teal);line-height:1.8;margin-bottom:15px}.quiz-active-note{margin:0 0 18px;font-size:12px}.quiz-history-row>b small{font-size:10px;text-align:right;color:var(--muted);margin-top:4px;font-weight:500}.quiz-stat small{line-height:1.7}
@media(max-width:1120px){.quiz-hero{grid-template-columns:minmax(0,1fr)}.quiz-stat{border-left:0;border-top:1px solid var(--line);padding:18px 0 0;text-align:left;grid-template-columns:auto minmax(0,1fr);align-items:center;column-gap:20px}.quiz-stat b{grid-row:1/3}.quiz-stat small{grid-column:2}.quiz-stat span{align-self:end}.quiz-stat small{align-self:start}}
@media(max-width:620px){.quiz-config{grid-template-columns:minmax(0,1fr);gap:14px}.quiz-book-choice strong{font-size:11px}.quiz-count-choice{max-width:none}.quiz-history-row{align-items:start}.quiz-history-row>span{min-width:0}.quiz-history-row small{line-height:1.7}.quiz-history-row>b{padding-top:1px}.quiz-stat span,.quiz-stat small{text-align:right}.quiz-result .button-row{width:100%}.quiz-result .button-row>.btn{width:100%}}

/* Keep saved results readable while giving deletion a separate touch target. */
.quiz-history-heading{flex-wrap:wrap}
.quiz-history-tools{display:flex;align-items:center;flex-wrap:wrap;gap:12px}
.quiz-history-item{display:grid;grid-template-columns:minmax(0,1fr) auto;align-items:center;gap:10px}
.quiz-history-row{min-width:0}
.quiz-history-row>span{min-width:0;overflow-wrap:anywhere}
.quiz-history-row>b{flex-shrink:0}
.quiz-history-delete.btn,.quiz-history-clear.btn{min-height:44px}
.quiz-history-delete{white-space:nowrap}
.quiz-delete-confirm{margin-top:22px}
.quiz-delete-confirm h2{font-size:23px;line-height:1.35}
@media(max-width:620px){.quiz-history-tools{width:100%;justify-content:space-between}.quiz-history-item{gap:8px}.quiz-history-delete.btn{padding:10px 11px;font-size:11px}.quiz-delete-confirm .button-row>.btn{width:100%}}

body.dark .quiz-history-delete.btn,body.dark .quiz-history-clear.btn,body.dark .quiz-delete-confirm-button.btn{background:var(--card);border-color:#b67b70;color:#f6b1a2}
body.dark .header-institute img{background:#fffefa;border-radius:50%;padding:2px}
 .quiz-delete-confirm-button.btn{background:var(--danger);border-color:var(--danger);color:#fff}
body.dark .quiz-delete-confirm-button.btn{background:var(--card);border-color:#b67b70;color:#f6b1a2}
@media(max-width:360px){.quiz-history-item{grid-template-columns:minmax(0,1fr);gap:6px}.quiz-history-delete{justify-self:end;margin-bottom:4px}}
/* Physics adaptation of the Isbot reader structure. */
.app-workspace{margin-left:250px;min-height:100vh}.topbar{display:flex;align-items:center;justify-content:space-between;padding:22px 42px;border-bottom:1px solid var(--line);min-height:78px}.top-tag{font-size:10px;letter-spacing:1.4px;color:var(--muted)}main{max-width:1260px;margin:0 auto;padding:38px 42px 55px;min-height:75vh}.page-footer{margin:0 42px;padding:22px 0;border-top:1px solid var(--line);font-size:12px;color:var(--muted)}.mobile-brand{display:none}.brand-mark{font-style:italic;color:var(--gold)}.intro{margin-bottom:28px}.intro p{color:var(--muted);max-width:740px}.welcome{background:var(--light);border:1px solid #d9e3d6;border-radius:17px;display:grid;grid-template-columns:1.4fr 1fr;gap:35px;padding:34px;margin-bottom:25px}.welcome h1{font-size:38px}.welcome p{color:var(--muted)}.welcome-art{display:grid;place-items:center;color:var(--teal)}.welcome-art .katex{font-size:2.5em}.btn,.tool{display:inline-flex;align-items:center;justify-content:center;gap:8px;background:var(--teal);border:1px solid var(--teal);color:white;border-radius:9px;padding:10px 17px;font-size:14px;min-height:43px;cursor:pointer}.btn.secondary,.tool{background:var(--card);color:var(--teal);border-color:var(--line)}.btn:disabled,.tool:disabled{cursor:default;opacity:.4}.stats-grid{display:grid;grid-template-columns:repeat(3,1fr);gap:16px;margin:20px 0 30px}.stat-card{background:var(--card);border:1px solid var(--line);border-radius:12px;padding:22px}.stat-card b{display:block;font-size:28px;letter-spacing:-1px}.stat-card span{font-size:12px;color:var(--muted)}.section-head{display:flex;justify-content:space-between;align-items:center;gap:16px;margin:28px 0 16px}.section-head h2{margin:0}.book-grid{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:18px}.book-card{background:var(--card);border:1px solid var(--line);border-radius:13px;overflow:hidden}.book-cover{min-height:190px;padding:25px;color:#fff;background:var(--navy);display:flex;flex-direction:column;justify-content:space-between}.book-cover.gold{background:#8b7243}.book-cover.sage{background:#597465}.book-cover .tiny{color:#d9d6c9}.book-cover h3{font:28px/1.2 Georgia;margin:14px 0}.book-cover .math{font-size:20px;color:var(--gold)}.book-card-body{padding:20px}.book-card-body p{font-size:13px;color:var(--muted);min-height:40px}.status{display:inline-block;border-radius:20px;background:var(--light);color:var(--teal);font-size:11px;padding:4px 10px}.book-card .btn{width:100%;margin-top:12px}.reading-row{display:flex;align-items:center;gap:20px;background:var(--card);border:1px solid var(--line);border-radius:12px;padding:20px;margin:12px 0;color:var(--ink)}.reading-row .number{font:25px Georgia;color:var(--teal)}.reading-row h3{margin:0 0 6px}.reading-row small{color:var(--muted)}.reading-row .chevron{margin-left:auto}.reader{display:grid;grid-template-columns:220px minmax(0,1fr);gap:22px}.reader-index{background:var(--card);border:1px solid var(--line);border-radius:11px;align-self:start;padding:20px;position:sticky;top:20px}.reader-index h2{font-size:16px;margin-bottom:18px}.reader-index a{display:block;padding:12px 10px;font-size:13px;border-radius:7px;color:var(--muted)}.reader-index a.active{background:var(--light);color:var(--teal);font-weight:650}.reader-tools{display:flex;align-items:center;justify-content:space-between;gap:10px;flex-wrap:wrap;border:1px solid var(--line);background:var(--card);border-radius:11px;padding:10px 12px;margin-bottom:15px}.tool-group{display:flex;align-items:center;gap:8px}.tool{padding:6px 10px;min-height:37px;font-size:13px}.reader-tools input{width:57px;min-height:37px;padding:5px 8px;text-align:center}.reader-tools small{color:var(--muted)}.sheet{background:var(--card);border:1px solid var(--line);border-radius:12px;padding:30px;overflow:hidden}.sheet h2{font-size:27px}.prose{font-size:calc(17px * var(--reader-zoom,1));line-height:1.85}.prose p{color:#405761}.math.block{display:block;background:var(--light);padding:17px;border-radius:8px;margin:20px 0;overflow-x:auto;text-align:center}.math.block .katex-display{margin:0}.callout{border-left:3px solid #c6ac68;padding:14px 18px;background:#f7f5e9;margin:20px 0;font-size:.92em}.callout strong{font-size:.8em;letter-spacing:.05em}.callout p{margin:8px 0 0}details{border-top:1px solid var(--line);padding:16px 0}summary{cursor:pointer;font-size:.95em;font-weight:600}details>p{margin-top:12px}.reader-bottom{display:flex;justify-content:space-between;align-items:center;margin:18px 0}.note-box,.panel{background:var(--card);border:1px solid var(--line);border-radius:12px;padding:24px;margin:20px 0}.note-box textarea{min-height:140px}.note-box label{font-weight:650;margin-bottom:7px}.note-box small{display:block;margin-top:7px;color:var(--muted)}.note-box[hidden]{display:none}.answer-row{display:flex;flex-wrap:wrap;gap:10px;align-items:center;margin:20px 0 8px}.answer-row label{font-size:12px}.answer-row input{width:120px}.feedback{min-height:30px;font-size:14px;margin-top:8px}.good{color:#216b43}.bad{color:#a44735}.filters{display:flex;gap:12px;margin:20px 0}.filters input{flex:1;min-width:0}.sim{background:var(--light);padding:24px;border-radius:12px;margin:20px 0}.sim label{display:flex;justify-content:space-between;font-size:14px}.sim input{width:100%;accent-color:var(--teal);padding:0;border:0;background:none}.track{height:50px;border-bottom:1px solid #9ab09d;position:relative;margin:18px 12px}.ball{position:absolute;bottom:0;width:24px;height:24px;border-radius:50%;background:var(--teal);transform:translateX(-50%)}.ticks{display:flex;justify-content:space-between;font:11px monospace;color:var(--muted)}.checklist label{display:flex;gap:10px;align-items:center;margin:12px 0;font-size:14px}.help{font-size:13px;color:var(--muted)}.hidden{display:none!important}.road-grid{display:grid;grid-template-columns:repeat(3,1fr);gap:20px}.road-grid .panel{margin:0}.road-grid p{font-size:14px;color:var(--muted)}.route-pills{display:flex;gap:8px;flex-wrap:wrap;margin:20px 0}.route-pills a{padding:7px 12px;background:var(--card);border:1px solid var(--line);border-radius:20px;font-size:12px}.bottom-nav{display:none}.side-equation .katex{font-size:1.2em}.empty{text-align:center;padding:40px;color:var(--muted)}.quiz-option{display:block;width:100%;text-align:left;border:1px solid var(--line);padding:13px;margin:8px 0;background:var(--card);color:var(--ink)}.quiz-option.chosen{background:var(--light);border-color:var(--teal)}.progress-bar{height:5px;background:var(--line);border-radius:5px;margin-top:13px;overflow:hidden}.progress-bar i{display:block;height:100%;background:var(--teal)}
@media(max-width:1000px){.sidebar{width:220px;padding:24px 17px}.app-workspace{margin-left:220px}main{padding:28px}.topbar{padding:20px 28px}.book-grid{grid-template-columns:repeat(2,1fr)}.reader{grid-template-columns:170px minmax(0,1fr);gap:15px}.reader-index{padding:14px}.sheet{padding:23px}.welcome{grid-template-columns:1fr}.welcome-art{display:none}.road-grid{grid-template-columns:1fr}}
@media(max-width:760px){.sidebar{display:none}.app-workspace{margin-left:0;padding-bottom:82px}.mobile-brand{display:block;font-size:19px;color:var(--ink);font-weight:750}.topbar{padding:17px 20px;min-height:64px}.top-tag{display:none}.breadcrumb{font-size:11px}.bottom-nav{position:fixed;bottom:0;left:0;right:0;display:flex;overflow-x:auto;gap:0;background:var(--card);border-top:1px solid var(--line);z-index:40;padding:5px 4px calc(5px + env(safe-area-inset-bottom));justify-content:space-around}.bottom-nav a{flex:0 0 14%;min-width:52px;display:flex;align-items:center;flex-direction:column;padding:5px 2px;color:var(--muted);font-size:10px}.bottom-nav a span{font-size:20px}.bottom-nav a.active{color:var(--teal);background:var(--light);border-radius:7px}.bottom-nav small{font-size:9px}main{padding:25px 18px;min-height:70vh}.page-footer{margin:0 18px;font-size:11px}.intro h1{font-size:28px}.welcome{padding:25px}.welcome h1{font-size:32px}.stats-grid{gap:8px}.stat-card{padding:15px 10px}.stat-card b{font-size:24px}.stat-card span{font-size:10px}.book-grid{grid-template-columns:1fr}.book-cover{min-height:155px}.reader{grid-template-columns:1fr}.reader-index{position:static;padding:12px;display:flex;overflow-x:auto;gap:6px}.reader-index h2{display:none}.reader-index a{white-space:nowrap;padding:8px 10px;font-size:11px}.reader-tools{padding:8px}.sheet{padding:22px 17px}.sheet h2{font-size:25px}.prose{font-size:calc(16px * var(--reader-zoom,1))}.reader-bottom{gap:8px}.reader-bottom .btn{font-size:12px;padding:9px 12px}.filters{flex-direction:column}.section-head h2{font-size:21px}.panel,.note-box{padding:20px}.nav-caption{margin-top:25px}}

/* Full physics library, isolated from the preserved introductory module. */
.library-toc{max-height:75vh;overflow:auto}.library-toc a{font-size:13px;line-height:1.5}.book-prose{overflow-wrap:anywhere;min-width:0;font-size:calc(17px * var(--reader-zoom,1));line-height:1.8}.book-prose img{display:block;max-width:100%;height:auto;margin:24px auto}.book-prose figure{margin:24px 0}.book-prose figcaption{font-size:.85em;color:var(--muted,#62655e);text-align:center}.book-prose .math.display,.book-prose .katex-display{display:block;overflow-x:auto;overflow-y:hidden;max-width:100%;padding:6px 0}.book-prose .math.inline{display:inline}.book-prose table{display:block;max-width:100%;overflow:auto;border-collapse:collapse;font-size:.9em}.book-prose th,.book-prose td{border:1px solid #dedfd7;padding:8px 12px}.book-prose h1{font-size:1.7em}.book-prose h2{font-size:1.4em}.book-prose h3{font-size:1.15em}.book-prose pre{white-space:pre-wrap}.math-error{color:#8b2c26;background:#fff3ef;font-family:monospace}.book-card h3{font-size:23px}.book-cover{min-height:205px}.reader>div{min-width:0}#library-note{display:block;width:100%;box-sizing:border-box;margin-top:12px;padding:14px;font:inherit;border:1px solid #cdd1c7;border-radius:10px}#library-search,#chapter-search,#bank-search,#bank-book{width:100%;box-sizing:border-box;font:inherit;padding:12px;margin:8px 0 20px;border:1px solid #d8dbd1;border-radius:10px;background:white;color:#26352e}#library-jump{width:64px;padding:8px}.reader-tools{flex-wrap:wrap;gap:10px}.book-prose a{overflow-wrap:anywhere}.book-prose [id]{scroll-margin-top:90px}.route-pills button{font:inherit}.book-card-body p{overflow-wrap:anywhere}.book-cover h3{overflow-wrap:anywhere}@media(max-width:760px){.library-toc{max-height:220px;position:static}.book-prose{font-size:calc(16px * var(--reader-zoom,1))}.book-prose h1{font-size:1.5em}.reader-tools{position:static}.reader-tools .tool-group{flex-wrap:wrap}.book-prose figure{margin:18px 0}.sheet{min-width:0}.book-cover{min-height:180px}}