.ch03-model { margin:1.5rem 0 1.8rem; }
.ch03-model iframe { width:100%; height:1100px; border:1px solid #d9e3e6; border-radius:10px; background:#f7f9f9; display:block; }
.ch03-model .model-caption { color:#4a6068; font-size:.88rem; margin:.6rem .25rem; line-height:1.6; }
.ch03-source { color:#63727a; font-size:.83rem; line-height:1.6; }
#chapter-exercises { scroll-margin-top:2rem; }
.chapter-references .reference-entry { padding-left:2rem; text-indent:-2rem; line-height:1.8; margin-bottom:.85rem; }
@media print { .ch03-model { display:none; } }

.ch03-citation { font-size:.75em; margin:0 .12em; white-space:nowrap; }

.ch03-math-note {border-left:3px solid #8d72aa;background:#f6f2f9;padding:.8rem 1.1rem;margin:1rem 0;color:#62487c;font-size:.94rem;}
.ch03-case-photo{max-width:760px;margin:1.4rem auto;border:1px solid #d5e0dc;border-radius:10px;overflow:hidden;}
.ch03-case-photo a{display:block;text-decoration:none;color:#294e43;}
.ch03-case-photo img{display:block;width:100%;max-height:350px;object-fit:cover;}
.ch03-case-photo strong{display:block;padding:.8rem 1rem;font-size:.93rem;}