*{box-sizing:border-box}body{margin:0;background:#f1f3f5;color:#203949;font-family:Arial,"PingFang SC","Microsoft YaHei",sans-serif;font-size:16px;line-height:1.6}a{color:inherit}button{font:inherit;cursor:pointer}header{height:82px;border-bottom:1px solid #dce3e7;background:#fafbfc;display:flex;align-items:center;justify-content:space-between;padding:0 max(24px,calc((100vw - 1220px)/2));gap:20px}.brand{display:flex;align-items:center;gap:13px;text-decoration:none;font-size:20px;font-weight:700}.logo{display:grid;place-items:center;width:42px;height:42px;background:#163e50;border-radius:10px;color:white;font:30px Georgia,serif}.languages{display:flex;gap:3px;border-radius:9px;padding:4px;background:#e8edf1;flex-shrink:0}.languages button{border:0;background:none;padding:7px 16px;border-radius:6px;color:#506779;font-size:14px}.languages [aria-pressed=true]{background:white;color:#164e5f;box-shadow:0 1px 5px #17374b15;font-weight:700}main{max-width:1300px;margin:auto;padding:36px 28px 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22px}.books{display:grid;grid-template-columns:repeat(4,minmax(0,1fr));gap:12px;position:relative}.book{--cover:#184c61;--cover-dark:#0e3041;--cover-light:#387085;--ink:#f1e7c6;--angle:-19deg;display:flex;align-items:center;flex-direction:column;min-width:0;text-decoration:none;padding:10px 0;border-radius:8px}.book:nth-child(2){--angle:11deg}.book:nth-child(3){--angle:-10deg}.book:nth-child(4){--angle:17deg}.book.unavailable{--cover:#78838b;--cover-dark:#4d5962;--cover-light:#96a1a7;--ink:#e5e8e9}.book-mount{width:clamp(150px,16vw,206px);aspect-ratio:5/7;position:relative;perspective:1100px;perspective-origin:50% -30%;margin:26px 0 38px;flex-shrink:0}.desk-shadow{position:absolute;inset:0;background:#3e3528;filter:blur(13px);opacity:.3;transform:translate(16px,24px) rotateX(48deg) rotateZ(var(--angle));border-radius:8px}.book-volume{position:absolute;inset:0;transform-style:preserve-3d;transform:rotateX(48deg) rotateZ(var(--angle));transition:transform .35s cubic-bezier(.2,.7,.2,1);will-change:transform}.available:hover .book-volume{transform:translateY(-10px) rotateX(43deg) rotateZ(var(--angle))}.available:hover .desk-shadow{opacity:.22;filter:blur(19px)}.back-cover{position:absolute;inset:0;background:var(--cover-dark);border-radius:3px 7px 7px 3px;box-shadow:6px 12px 18px #2f2c2445}.paper-block{position:absolute;inset:4px 4px 4px 7px;background:#f7f0df;transform:translateZ(12px)}.page-edge{position:absolute;background:repeating-linear-gradient(90deg,#ddd4c4 0px,#f9f3e8 1px,#eee6d8 2px);backface-visibility:visible}.edge-right{width:22px;top:4px;bottom:4px;left:calc(100% - 4px);transform-origin:left center;transform:translateZ(23px) rotateY(90deg)}.edge-bottom{height:22px;left:7px;right:4px;top:calc(100% - 4px);transform-origin:center top;transform:translateZ(23px) rotateX(-90deg);background:repeating-linear-gradient(0deg,#d5ccba 0px,#fcf6eb 1px,#eee6d8 2px)}.spine{position:absolute;top:0;bottom:0;left:0;width:24px;background:linear-gradient(90deg,var(--cover-dark),var(--cover));transform-origin:left center;transform:rotateY(-90deg);border-radius:3px 0 0 3px;display:grid;place-items:center;overflow:hidden;color:var(--ink)}.spine span{font-size:10px;writing-mode:vertical-rl;letter-spacing:.17em;white-space:nowrap}.front-cover{position:absolute;inset:0;transform:translateZ(24px);transform-origin:left center;transform-style:preserve-3d;border-radius:3px 7px 7px 3px}.cover-face,.inner-cover{position:absolute;inset:0;backface-visibility:hidden;-webkit-backface-visibility:hidden;border-radius:3px 7px 7px 3px}.cover-face{background:linear-gradient(90deg,#0003,transparent 5%,#ffffff1b 6%,transparent 8%),repeating-linear-gradient(90deg,#ffffff03 0px,#00000003 1px,transparent 2px,transparent 4px),var(--cover);color:var(--ink);display:flex;flex-direction:column;padding:20px 18px 18px 25px;box-shadow:inset -1px 0 2px #ffffff35,inset 0 0 0 1px #ffffff15,2px 2px 4px #0002}.cover-face:after{content:'';position:absolute;inset:10px 9px 10px 16px;border:1px solid #dec89045;pointer-events:none}.cover-top{display:flex;justify-content:space-between;gap:10px;font-size:10px;letter-spacing:.09em;opacity:.7}.edition{font-family:Georgia,serif}.cover-title{margin-top:26px}.cover-title h2{font-family:"Songti SC",Georgia,serif;font-weight:600;font-size:27px;line-height:1.4;letter-spacing:.06em;margin:0}.cover-title p{font:11px/1.5 Georgia,"Songti SC",serif;opacity:.8;margin:10px 0 0}.cover-rule{width:26px;height:1px;background:currentColor;opacity:.55;margin-top:18px}.formula{font:italic clamp(21px,2.4vw,33px)/1.25 Georgia,serif;margin:auto 0 12px;opacity:.65;white-space:nowrap}.cover-footer{font-size:9px;letter-spacing:.09em;opacity:.6}.inner-cover{background:linear-gradient(90deg,#d5c6a3,#ede2c7 15%,#f1e8d4);transform:rotateY(180deg);border:7px solid var(--cover-dark);box-shadow:inset -7px 0 16px #695d3b33}.inside-page,.turn-leaf{position:absolute;inset:4px 5px 5px 6px;transform-origin:left center;transform-style:preserve-3d}.inside-page{transform:translateZ(20px);background:linear-gradient(90deg,#d5cbb7,#fffcf2 12%,#fffaf0);padding:22px;color:#3a4650;font-family:Georgia,"Songti SC",serif;overflow:hidden}.paper-kicker{font:9px Arial,sans-serif;letter-spacing:.05em;color:#828372}.inside-page h3{font-size:27px;margin:20px 0 10px;font-weight:400}.paper-rule{height:1px;background:#b0ab9a}.inside-page ol{margin:14px 0 0;padding:0;list-style:none;font:13px/2.15 Arial,"PingFang SC",sans-serif}.inside-page li{border-bottom:1px solid #dad5c455}.turn-leaf{transform:translateZ(22px)}.leaf-front,.leaf-back{position:absolute;inset:0;backface-visibility:hidden;-webkit-backface-visibility:hidden;background:linear-gradient(90deg,#ded5c2,#fffdf5 10%,#fbf7e9);box-shadow:1px 0 2px #62563d30}.leaf-front{display:flex;flex-direction:column;align-items:center;justify-content:center;text-align:center;padding:20px;color:#3c5963}.leaf-front>span{font-size:8px;letter-spacing:.1em;opacity:.6}.leaf-front h3{font:24px/1.4 Georgia,"Songti SC",serif;margin:25px 0 8px}.leaf-front p{font:12px/1.4 Georgia,"Songti SC",serif;margin:0}.leaf-front i{font:italic 27px Georgia,serif;margin-top:42px;color:#899492}.leaf-back{transform:rotateY(180deg);background:linear-gradient(90deg,#faf5e8,#fffdf4 90%,#d9ceba)}.book-label{text-align:center;display:flex;flex-direction:column;align-items:center;gap:6px;max-width:100%;padding:0 4px}.book-label strong{font-weight:500;font-size:17px;line-height:1.4}.status{font-size:13px;color:#657580;border:1px solid #b0afa644;padding:3px 12px;border-radius:20px;background:#faf9f444}.available .status{color:#21596a;border-color:#48798a50;background:#f2f8f8bb}.available:hover .status{background:#184c61;color:#fff}.unavailable .book-label{color:#6d777d}.selected-book .book-volume,.selected-book .desk-shadow{visibility:hidden}.book:focus-visible,button:focus-visible,a:focus-visible{outline:3px solid #ca9132;outline-offset:5px}footer{display:flex;justify-content:space-between;gap:20px;font-size:12px;color:#81909b;padding:25px 10px 0}.sr-only{position:absolute;width:1px;height:1px;padding:0;margin:-1px;overflow:hidden;clip:rect(0,0,0,0);white-space:nowrap;border:0}#book-reader{position:fixed;inset:0;margin:0;padding:0;width:100%;height:100%;max-width:none;max-height:none;border:0;overflow:hidden;background:transparent;color:#fff;perspective:1800px}#book-reader::backdrop{background:#142331b3;backdrop-filter:blur(7px);animation:backdrop-in .3s ease-out}.reader-actions{position:fixed;top:22px;right:24px;z-index:5;display:flex;align-items:center;gap:24px}.reader-actions a{font-size:14px;color:#fff;text-decoration:none;border-bottom:1px solid #ffffff66}.reader-actions button{width:40px;height:40px;border:1px solid #ffffff60;border-radius:50%;color:white;background:#ffffff10;font-size:28px;line-height:1}#book-actor{--cover:#184c61;--cover-dark:#0e3041;--cover-light:#387085;--ink:#f1e7c6;position:fixed;transform-style:preserve-3d;perspective:1800px;perspective-origin:50% 45%}#book-actor .book-volume{transition:none}#book-actor .cover-title h2{font-size:clamp(20px,3vw,36px)}#book-actor .cover-title p{font-size:13px}#book-actor .cover-top{font-size:12px}#book-actor .formula{font-size:36px}#book-actor .inside-page{padding:26px}html[lang=en] .cover-title h2{font-size:25px;letter-spacing:0}html[lang=en] .cover-title p{font-size:14px}html[lang=en] #book-actor .cover-title h2{font-size:clamp(18px,2.5vw,32px)}@keyframes backdrop-in{from{background:#14233100;backdrop-filter:blur(0)}to{background:#142331b3;backdrop-filter:blur(7px)}}@media(max-width:1050px){.books{grid-template-columns:repeat(2,minmax(0,1fr));gap:20px}.book-mount{width:210px;margin:24px 0 30px}.desk{padding:20px 20px 28px}.book{padding:4px 0 12px}.desk{min-height:auto}}@media(max-width:600px){header{height:72px;padding:0 18px}.brand{font-size:17px;gap:9px}.logo{width:35px;height:35px;font-size:25px}.languages button{padding:6px 10px}main{padding:26px 14px 20px}.heading{margin:0 4px 22px;gap:12px}h1{font-size:29px}.eyebrow{font-size:10px}.legend{font-size:11px;gap:5px}.legend-color.pending{margin-left:4px}.desk{padding:16px 8px 20px;border-bottom-width:9px}.books{gap:18px 6px}.book-mount{width:min(34vw,172px);margin:12px 0 20px}.book-volume{transform:rotateX(44deg) rotateZ(var(--angle))}.cover-face{padding:14px 10px 12px 17px}.cover-title{margin-top:15px}.cover-title h2{font-size:21px;line-height:1.35}.cover-title p{font-size:9px;margin-top:7px}.cover-top{font-size:8px}.cover-footer{font-size:7px}.cover-rule{margin-top:12px;width:20px}.formula{font-size:21px;margin-bottom:8px}.cover-face:after{inset:7px 6px 7px 11px}.book-label strong{font-size:15px}.status{font-size:12px;padding:2px 9px}.book-label{gap:5px}.inside-page{padding:12px}.reader-actions{top:16px;right:16px;gap:18px}#book-actor .cover-face{padding:18px 14px 16px 20px}#book-actor .cover-top{font-size:9px}#book-actor .cover-title h2{font-size:23px}#book-actor .cover-title p{font-size:10px}#book-actor .formula{font-size:23px}#book-actor .inside-page{padding:14px}.inside-page h3{font-size:23px;margin:12px 0 8px}.inside-page ol{font-size:10px;line-height:1.9}.paper-kicker{font-size:7px}.leaf-front{padding:10px}.leaf-front h3{font-size:21px;margin-top:14px}.leaf-front p{font-size:10px}.leaf-front i{font-size:22px;margin-top:25px}html[lang=en] .brand{font-size:14px;max-width:168px;line-height:1.3}html[lang=en] .brand .logo{flex-shrink:0}html[lang=en] .cover-title h2{font-size:18px}html[lang=en] .cover-title p{font-size:11px}html[lang=en] .heading{align-items:start;flex-direction:column;gap:10px}html[lang=en] #book-actor .cover-title h2{font-size:20px}footer{padding:20px 4px 0;font-size:11px}}@media(prefers-reduced-motion:reduce){*{transition:none!important;animation:none!important}}
.cover-face{overflow:hidden}[data-course="differential-geometry"] .formula{font-size:clamp(13px,1.65vw,22px)}

/* The science covers remain vector-sharp throughout the opening movement. */
[data-course="physics"] .cover-face{padding:0;background:#071a27}
.physics-cover-art{display:block;width:100%;height:100%;object-fit:fill}
[data-course="physics"] .cover-face:after{display:none}
.math-cover-art{width:100%;height:36%;margin:14px 0 0;fill:none;stroke:currentColor;stroke-width:1;opacity:.6}
.book.unavailable{--cover:#50626c;--cover-dark:#2e414e;--ink:#e0d7bf}
[data-course="linear-algebra"]{--cover:#4b6464;--cover-dark:#2a4344}
[data-course="differential-geometry"]{--cover:#5c596b;--cover-dark:#373445}
.book:not([data-course="physics"]) .cover-top{font-size:8px;letter-spacing:.04em;gap:2px}
.book:not([data-course="physics"]) .formula{font-size:20px;margin:12px 0 10px}
#book-actor{pointer-events:none;z-index:2}
#book-actor .back-cover,#book-actor .paper-block,#book-actor .page-edge,#book-actor .spine{display:none}
#book-reader{background:#03090fe8}
#opening-cinema{position:fixed;background:#03090f;overflow:hidden;z-index:1}
#opening-cinema[hidden]{display:none}
#opening-video{display:block;width:100%;height:100%;object-fit:contain;background:#03090f}
.cinema-feedback{position:absolute;left:20px;right:20px;bottom:72px;text-align:center;pointer-events:none}
#video-message:empty{display:none}#video-message{display:inline-block;background:#071a27df;border-radius:8px;padding:8px 16px;color:#f2e6cc;font-size:14px}
#start-video{pointer-events:auto;border:1px solid #d8be85;border-radius:30px;background:#102c3e;color:#f5e6c3;padding:12px 24px}
.reader-actions{background:#05121cca;padding:8px 12px;border-radius:32px}.reader-actions button{flex-shrink:0}
@media(min-width:1051px){.book-mount{width:clamp(170px,18vw,236px)}.desk{padding-top:40px;padding-bottom:28px}}
@media(max-width:600px){.book:not([data-course="physics"]) .cover-top{font-size:6px}.book:not([data-course="physics"]) .formula{font-size:16px}.math-cover-art{margin-top:8px}.reader-actions{top:10px;right:10px;gap:12px}.reader-actions a{font-size:12px}}

/* Flexible cover, with a separate printed face and a warm paper reverse. */
#book-actor .cover-face{padding:0}
.curl-sheet{position:absolute;inset:0;transform-style:preserve-3d}
.curl-strip{position:absolute;left:0;top:0;transform-origin:0 50%;transform-style:preserve-3d;will-change:transform}
.curl-front,.curl-back{position:absolute;inset:0;backface-visibility:hidden;-webkit-backface-visibility:hidden}
.curl-front{background-image:url('./physics-cover.svg?v=20260925-curl2');background-repeat:no-repeat}
.curl-back{transform:rotateY(180deg);background:repeating-linear-gradient(0deg,#e7ddc8 0px,#eee5d4 2px,#e7ddc8 4px)}
.curl-shade{position:absolute;inset:0;background:#000;pointer-events:none}

#book-reader[data-phase="turning"] .cinema-feedback,#book-reader[data-phase="turned"] .cinema-feedback{visibility:hidden}
#book-reader[data-phase="turning"] #opening-cinema,#book-reader[data-phase="turned"] #opening-cinema{pointer-events:none}

/* Approved transparent E-Phi mark and Wenknowledge name. */
header .brand{gap:12px;white-space:nowrap}
header .logo{display:block;width:52px;height:52px;object-fit:contain;flex-shrink:0;background:transparent;border-radius:0}
@media(max-width:600px){header .brand{gap:8px}header .logo{width:42px;height:42px}html[lang=en] header .brand{max-width:none}}
/* Keep the studio credit beside the brand, with natural wrapping on small screens. */
header{height:auto;min-height:82px;padding-top:12px;padding-bottom:12px;flex-wrap:wrap}
header .brand{min-width:0;flex:1 1 260px}
header .brand-copy{display:flex;align-items:baseline;flex-wrap:wrap;gap:3px 18px;min-width:0}
header .brand-studio{font-size:15px;font-weight:400;line-height:1.6;color:#536b78;white-space:normal}
header .languages{margin-left:auto}
@media(max-width:600px){header{min-height:72px;gap:10px}header .brand-studio{font-size:13px}header .brand-copy{gap:2px 12px}}