diff --git a/src/components/learn/References.astro b/src/components/learn/References.astro
index 341edd8..a28f8fb 100644
--- a/src/components/learn/References.astro
+++ b/src/components/learn/References.astro
@@ -57,10 +57,25 @@ const citations = [...citationIndex.values()].sort((a, b) => a.n - b.n);
 )}
 
 <style>
-  /* Links inside `formatReference()` output (DOI/ISBN/URL anchors) carry no
-     color class - they rely on the browser's default anchor color, left
-     untouched in light mode for pixel parity. Dark mode gets the standard
-     crystal-400 / gold-hover treatment used everywhere else in prose links. */
+  /* Links inside `formatReference()` output (DOI/ISBN/URL anchors) previously
+     carried no color class, so with the site's Tailwind preflight reset
+     (`a { color: inherit }`) they rendered in the same slate-600 body-text
+     color as the surrounding <span> with no underline — visually
+     indistinguishable from plain text in light mode. Scope the fix to
+     `a[href^="http"]`: every DOI/ISBN/URL anchor produced by formatReference()
+     is an absolute http(s) link, while the backlink (`href="#citeref-..."`)
+     uses a fragment href and already has its own explicit slate/crystal
+     styling above, so this selector cannot touch it. */
+  :global(.references a[href^="http"]) {
+    color: #0369a1; /* crystal-700, matches prose-a:text-crystal-700 */
+    text-decoration: underline;
+    text-decoration-color: rgba(3, 105, 161, 0.4);
+    text-underline-offset: 2px;
+  }
+  :global(.references a[href^="http"]:hover) {
+    color: #075985; /* crystal-800 */
+    text-decoration-color: currentColor;
+  }
   :global([data-theme='dark'] .references a) {
     color: #38bdf8; /* crystal-400 */
   }
@@ -73,13 +88,18 @@ const citations = [...citationIndex.values()].sort((a, b) => a.n - b.n);
      the row so it's obvious which reference was jumped to. `:target` only
      matches the element whose id equals the URL fragment (the `<li
      id="cite-{id}">` rendered above), so this only ever highlights one row
-     at a time. */
+     at a time.
+
+     Duration is 2.6s total: the first 35% (~0.9s) holds at near-full
+     intensity so the flash is reliably noticed even if the reader glances
+     away briefly, then eases out over the remaining ~1.7s. (Originally a
+     flat 1.2s ease-out, which read as too brief to reliably catch.) */
   :global(.references li:target) {
-    animation: cite-target-flash 1.2s ease-out;
+    animation: cite-target-flash 2.6s ease-out;
     border-radius: 0.375rem;
   }
   @keyframes cite-target-flash {
-    0% {
+    0%, 35% {
       background-color: rgba(3, 105, 161, 0.16); /* crystal-700/16 */
       box-shadow: -3px 0 0 0 #0369a1; /* crystal-700 left accent */
     }
@@ -92,7 +112,7 @@ const citations = [...citationIndex.values()].sort((a, b) => a.n - b.n);
     animation-name: cite-target-flash-dark;
   }
   @keyframes cite-target-flash-dark {
-    0% {
+    0%, 35% {
       background-color: rgba(56, 189, 248, 0.14); /* crystal-400/14 */
       box-shadow: -3px 0 0 0 #38bdf8; /* crystal-400 left accent */
     }
diff --git a/src/components/learn/SectionRenderer.astro b/src/components/learn/SectionRenderer.astro
index 70e005f..45ae68f 100644
--- a/src/components/learn/SectionRenderer.astro
+++ b/src/components/learn/SectionRenderer.astro
@@ -48,8 +48,29 @@ interface Subsection {
   table?: Table;
   system?: CrystalSystem;
   cdl?: string;
+  comparison?: Comparison;
+  callout?: CalloutData;
+  crystal?: Crystal;
 }
 
+// Keys of Subsection that the renderer below actually knows how to draw.
+// Used only for the DEV-mode "unhandled subsection key" warning so a future
+// authored field silently vanishing (like comparison/callout/crystal did
+// before this fix) gets caught immediately instead of shipping unnoticed.
+const KNOWN_SUBSECTION_KEYS = new Set([
+  'title',
+  'content',
+  'items',
+  'table',
+  'system',
+  'cdl',
+  'comparison',
+  'callout',
+  'crystal',
+  // Added by the pre-render step below, not authored content.
+  'renderedContent',
+]);
+
 interface Section {
   title: string;
   id?: string;
@@ -105,16 +126,35 @@ const renderMarkdown = async (text: string) => {
 const sectionContent = section.content ? await renderMarkdown(section.content) : null;
 const calloutContent = section.callout?.text ? await renderMarkdown(section.callout.text) : null;
 
-// Pre-render subsection content
+// Pre-render subsection content (including subsection-level callout text,
+// which needs the same markdown + mineral-linking treatment as section
+// callouts).
 const subsectionContent = section.subsections
   ? await Promise.all(
       section.subsections.map(async (sub) => ({
         ...sub,
         renderedContent: sub.content ? await renderMarkdown(sub.content) : null,
+        renderedCalloutContent: sub.callout?.text ? await renderMarkdown(sub.callout.text) : null,
       }))
     )
   : null;
 
+// DEV-only guard: warn when an authored subsection carries a key this
+// renderer doesn't know how to draw, so a future silent content-drop (like
+// comparison/callout/crystal being stripped before this fix) surfaces
+// immediately in the console instead of shipping unnoticed.
+if (import.meta.env.DEV && section.subsections) {
+  for (const sub of section.subsections) {
+    const unknownKeys = Object.keys(sub).filter((key) => !KNOWN_SUBSECTION_KEYS.has(key));
+    if (unknownKeys.length > 0) {
+      console.warn(
+        `[SectionRenderer] Subsection "${sub.title}" in section "${section.title}" has ` +
+          `unhandled key(s): ${unknownKeys.join(', ')}. This content will not render.`
+      );
+    }
+  }
+}
+
 // Build section-level citation cluster HTML when section.citations is present.
 function buildCitationCluster(ids: string[]): string {
   if (!citationIndex || ids.length === 0) return '';
@@ -196,8 +236,14 @@ const sectionCitationCluster =
   )}
 
   {subsectionContent && subsectionContent.map(sub => {
-    // Check if this subsection is a crystal system
-    const detectedSystem = sub.system || detectCrystalSystem(sub.title);
+    // Check if this subsection is a crystal-system SUMMARY card. Subsections
+    // that author an explicit `crystal:` block (a CDL demo + caption, e.g.
+    // "Cubic Examples" in crystallography-advanced.yaml's "CDL Crystal
+    // Examples" section) must NOT be diverted here even though
+    // detectCrystalSystem() pattern-matches a system name in their title —
+    // they render via CrystalDemo in the regular-subsection branch below,
+    // same as section-level `section.crystal`.
+    const detectedSystem = sub.crystal ? null : (sub.system || detectCrystalSystem(sub.title));
 
     if (detectedSystem) {
       // Render as a crystal system card
@@ -218,6 +264,11 @@ const sectionCitationCluster =
             <h3 class="text-lg font-semibold text-slate-800 dark:text-cream-primary">{sub.title}</h3>
           </div>
           <div class="p-4">
+            {sub.callout && sub.renderedCalloutContent && (
+              <Callout variant={sub.callout.type} title={sub.callout.title}>
+                <Fragment set:html={sub.renderedCalloutContent} />
+              </Callout>
+            )}
             {sub.renderedContent && (
               <div class="prose prose-slate prose-lg max-w-none mb-4
                           prose-headings:text-slate-900 dark:prose-headings:text-cream-primary
@@ -227,12 +278,22 @@ const sectionCitationCluster =
                           prose-a:text-crystal-700 dark:prose-a:text-crystal-400 dark:hover:prose-a:text-crystal-300 dark:hover:prose-a:decoration-gold"
                    set:html={sub.renderedContent} />
             )}
+            {sub.crystal && (
+              <CrystalDemo
+                cdl={sub.crystal.cdl}
+                caption={sub.crystal.caption}
+                interactive={sub.crystal.interactive ?? true}
+              />
+            )}
             {sub.items && <PropertyList items={sub.items} headingLevel={4} citationIndex={citationIndex} />}
             {sub.table && (
               <div class="table-scroll-hint relative">
                 <DataTable headers={sub.table.headers} rows={sub.table.rows} caption={sub.table.caption} citationIndex={citationIndex} />
               </div>
             )}
+            {sub.comparison && (
+              <ComparisonBlock items={sub.comparison.items} headingLevel={4} />
+            )}
           </div>
         </div>
       );
diff --git a/src/content/config.ts b/src/content/config.ts
index 6789291..513c470 100644
--- a/src/content/config.ts
+++ b/src/content/config.ts
@@ -120,11 +120,30 @@ const imageSchema = z.object({
 });
 
 // Schema for subsections (nested H3 content)
+// NOTE: comparison/callout/crystal reuse the exact section-level schemas
+// (comparisonSchema/calloutSchema/crystalSchema, defined above) because
+// authored content nests these blocks under `subsections:` using the same
+// shape as their section-level counterparts (verified against
+// fundamentals/crystallography-advanced.yaml "Open vs Closed Forms" /
+// "Cubic Examples" and equipment/other-tools.yaml callout subsections).
+//
+// `system`/`cdl` are a second, older, flatter shape for the same
+// "render a crystal demo" intent — authored directly (not nested under
+// `crystal:`) by fundamentals/crystal-systems.yaml, e.g.:
+//   subsections: [{ title: ..., system: cubic, cdl: "cubic[m3m]:..." }]
+// Both shapes were previously stripped by zod (unknown keys are dropped by
+// default) before ever reaching SectionRenderer.astro, even though the
+// Subsection TS interface there already declared them.
 const subsectionSchema = z.object({
   title: z.string(),
   content: z.string().optional(),
   items: z.array(itemSchema).optional(),
   table: tableSchema.optional(),
+  comparison: comparisonSchema.optional(),
+  callout: calloutSchema.optional(),
+  crystal: crystalSchema.optional(),
+  system: z.enum(['cubic', 'hexagonal', 'trigonal', 'tetragonal', 'orthorhombic', 'monoclinic', 'triclinic']).optional(),
+  cdl: z.string().optional(),
 });
 
 // Main section schema
diff --git a/src/pages/learn/index.astro b/src/pages/learn/index.astro
index 638e4bb..873cc2e 100644
--- a/src/pages/learn/index.astro
+++ b/src/pages/learn/index.astro
@@ -272,18 +272,28 @@ const iconPaths: Record<string, string> = {
       <div class="max-w-3xl pb-8 border-b border-slate-200 dark:border-coffee-border">
         <h1 class="text-4xl font-bold text-slate-900 dark:text-cream-primary">Learn Gemmology</h1>
         <p class="mt-1 text-lg font-medium text-crystal-700 dark:text-crystal-300">Free FGA exam preparation and structured study guide</p>
-        <p class="mt-4 text-base text-slate-600 dark:text-cream-secondary">
+        <p class="mt-4 text-base text-slate-600 dark:text-cream-secondary max-w-2xl">
           A structured, free study path for the Gem-A FGA Foundation and Diploma curriculum:
-          {totalTopicCount} articles across eight categories: crystal systems, physical and optical
+          {totalTopicCount} articles across eight categories — crystal systems, physical and optical
           properties, equipment, gem species, identification, phenomena, geographic origin, market
-          and grading, and gem care. Each article is paired with browser-based tools (refractometer
-          simulator, spectroscope band-matcher, treatment wizard, proportion analyzer) and an
-          SM-2-scheduled practice quiz so that theory and applied identification reinforce each
-          other in one place. Articles include pretest questions that count toward spaced-repetition
-          scheduling and link out to the canonical mineral database, so the same hardness, refractive
-          index, and birefringence values support reading, testing, and recall. Use the category grid
-          below to browse by topic, or start the daily review queue if you have an active study
-          schedule.
+          and grading, and gem care.
+        </p>
+        <ul class="mt-4 grid gap-x-6 gap-y-2 sm:grid-cols-3 text-sm text-slate-600 dark:text-cream-secondary">
+          <li class="flex items-start gap-2">
+            <span aria-hidden="true" class="mt-1 h-1.5 w-1.5 flex-shrink-0 rounded-full bg-crystal-700 dark:bg-crystal-300"></span>
+            <span>Paired with browser-based tools — refractometer simulator, spectroscope band-matcher, treatment wizard, proportion analyzer</span>
+          </li>
+          <li class="flex items-start gap-2">
+            <span aria-hidden="true" class="mt-1 h-1.5 w-1.5 flex-shrink-0 rounded-full bg-crystal-700 dark:bg-crystal-300"></span>
+            <span>Pretest questions in every article feed an SM-2-scheduled spaced-repetition quiz</span>
+          </li>
+          <li class="flex items-start gap-2">
+            <span aria-hidden="true" class="mt-1 h-1.5 w-1.5 flex-shrink-0 rounded-full bg-crystal-700 dark:bg-crystal-300"></span>
+            <span>Linked to the canonical mineral database, so hardness, RI, and birefringence values stay consistent everywhere</span>
+          </li>
+        </ul>
+        <p class="mt-4 text-sm text-slate-600 dark:text-cream-secondary">
+          Use the category grid below to browse by topic, or start the daily review queue if you have an active study schedule.
         </p>
       </div>
 
diff --git a/tailwind.config.mjs b/tailwind.config.mjs
index 42eb8c1..e512188 100644
--- a/tailwind.config.mjs
+++ b/tailwind.config.mjs
@@ -183,6 +183,28 @@ export default {
             p: {
               maxWidth: 'none',
             },
+            // NOTE: the DEFAULT block above defines custom `ol`, `ol > li`,
+            // `ol > li::before` (counter badge) and `ul > li::before` rules,
+            // but @tailwindcss/typography generates `.prose-lg` as a fully
+            // separate ruleset from its own built-in `lg` size config — it
+            // does NOT inherit DEFAULT's custom overrides. That built-in `lg`
+            // config sets its own `padding-inline-start` on `ol`, `ul`,
+            // `ol > li` and `ul > li` (~0.44em), and because `.prose-lg`'s
+            // rules are emitted after `.prose`'s in the stylesheet, its
+            // logical `padding-inline-start` wins the cascade over our
+            // physical `padding-left` from DEFAULT (per the CSS Logical
+            // Properties spec, a logical/physical pair for the same edge is
+            // resolved by cascade order, not by property name) — even though
+            // both were set with equal selector specificity. That silently
+            // shrank the reserved space for the absolute-positioned counter
+            // badge under `prose-lg`, so the badge (1.5em wide) overlapped
+            // the first ~19px of ordered-list text (regression from PR #55
+            // switching body copy to `prose-lg`). Fix: replicate the same
+            // rules here with BOTH the physical and logical property set,
+            // so this override always wins regardless of which one the
+            // browser resolves the box edge from. `ul > li` needed the same
+            // treatment (residual ~8px indent creeping back in), which is
+            // why it already carried `paddingInlineStart: '0'` below.
             'ul': {
               paddingLeft: '0',
               paddingInlineStart: '0',
@@ -191,7 +213,40 @@ export default {
             },
             'ul > li': {
               paddingLeft: '0',
+              paddingInlineStart: '0',
               marginLeft: '0',
+              marginInlineStart: '0',
+            },
+            'ul > li::before': {
+              content: 'none',
+            },
+            'ol': {
+              listStyle: 'none',
+              paddingLeft: '0',
+              paddingInlineStart: '0',
+              counterReset: 'item',
+            },
+            'ol > li': {
+              position: 'relative',
+              paddingLeft: '2em',
+              paddingInlineStart: '2em',
+              counterIncrement: 'item',
+            },
+            'ol > li::before': {
+              content: 'counter(item)',
+              position: 'absolute',
+              left: '0',
+              top: '0',
+              width: '1.5em',
+              height: '1.5em',
+              fontSize: '0.75em',
+              fontWeight: '600',
+              color: '#0369a1',
+              backgroundColor: '#e0f2fe',
+              borderRadius: '0.25em',
+              display: 'flex',
+              alignItems: 'center',
+              justifyContent: 'center',
             },
           },
         },