.concept h4 { margin:30px 0 16px; font-family:var(--sans); font-size:18px; line-height:1.8; color:var(--plum-deep); }
.concept p { line-height:2.05; margin-bottom:1.25em; }
.chapter-source { margin-top:23px; border-top:1px solid var(--line); padding-top:12px; color:var(--muted); font-size:12px; }
.chapter-source summary { cursor:pointer; min-height:44px; padding:10px 0; }
.chapter-source p { font-size:12px; }
.takeaways > p:not(.eyebrow) { font-size:16px; }
.afterthought { margin-top:22px; }
.toc a { font-size:13px; line-height:1.7; }
@media(max-width:720px) { .toc ol { grid-template-columns:minmax(0,1fr); } .concept h4 { font-size:17px; margin-top:26px; } }

.reading-index > summary { display:none; cursor:pointer; min-height:44px; padding:10px 7px; color:var(--plum-deep); }
@media(max-width:720px) { .reading-index > summary { display:list-item; margin-left:18px; } }

.purchase-panel { display:grid; grid-template-columns:96px minmax(0,1fr); gap:22px; align-items:center; margin:18px 0 24px; }
.purchase-cover { display:block; width:96px; height:auto; box-shadow:0 5px 12px #4b3d2a20; }
.purchase-content { min-width:0; }
.purchase-book-title { font-size:16px; font-weight:700; line-height:1.7; margin-bottom:14px; }
.purchase-book-title span { display:block; color:var(--muted); font-size:12px; font-weight:400; margin-top:3px; }
@media(max-width:540px) {
 .purchase-panel { grid-template-columns:72px minmax(0,1fr); gap:15px; align-items:start; }
 .purchase-cover { width:72px; }
 .purchase-book-title { font-size:14px; }
 .purchase-options a { flex-direction:column; gap:2px; padding:9px 6px; }
 .purchase-options a span { font-size:12px; }
}