Great share—here’s a focused, drop-in tune-up for the LOC homepage you pasted. I’ve prioritized by impact (accessibility & Core Web Vitals first), and kept everything backward-compatible with your current stack.

1) Accessibility & motion-safety (top win)

Respect “Reduce Motion” and stop the hero carousel

<style>
@media (prefers-reduced-motion: reduce) {
  * { animation: none !important; transition: none !important; }
  .featured .featured-slider { animation: none !important; }
}
</style>

<script>
  // Pause the slider if the user prefers reduced motion
  (function () {
    var m = window.matchMedia && matchMedia('(prefers-reduced-motion: reduce)');
    function maybePause() {
      var $ = window.jQuery;
      if (!($ && $('.featured-slider').slick)) return;
      if (m && m.matches) {
        $('.featured-slider').slick('slickPause')
                             .slick('slickSetOption','autoplay',false,true);
        var btn = document.getElementById('play-pause-button');
        if (btn) { btn.classList.add('paused'); btn.setAttribute('aria-label','Play'); }
      }
    }
    document.addEventListener('DOMContentLoaded', maybePause);
    if (m) m.addEventListener('change', maybePause);
  }());
</script>

Landmark labeling (screen reader clarity)

<nav class="header-menu" aria-labelledby="header-menu-button" aria-label="Primary"></nav>
<nav class="breadcrumbs-wrapper" aria-label="Breadcrumb">…</nav>
<nav class="horizontal-scrolling-navigation-wrapper" aria-label="Programs & services">…</nav>
<footer class="footer" role="contentinfo" aria-label="Site footer">…</footer>
<section class="featured" aria-label="Featured items">…</section>
<section class="trending" aria-label="Trending">…</section>
<section class="your-library" aria-label="Your Library">…</section>
<section class="public-domain" aria-label="Free to Use and Reuse: Teachers and Students">…</section>

Search form: unique, explicit label on the input

(You already provide a visible label; keep it tied to the input via for/id.)

<label for="search" class="screen-readers-only">Search the Library of Congress</label>
<input type="search" id="search" name="q" … />

2) LCP / Core Web Vitals: make the hero image “priority”

Your LCP is almost certainly the first slide image. Hint it to the browser:

<link rel="preload" as="image"
      href="/static/home/images/featured/nbf/2025-natbookfest2_1200x560.jpg"
      fetchpriority="high" imagesrcset="/static/home/images/featured/nbf/2025-natbookfest2_1200x560.jpg 1x">

Also add fetchpriority="high" on that <img> itself:

<img src="/static/home/images/featured/nbf/2025-natbookfest2_1200x560.jpg"
     alt="Library of Congress National Book Festival 25-year multi-color graphic"
     fetchpriority="high">

(Keep loading="lazy" on below-the-fold images; you already do this in “Trending”.)

3) Head/meta correctness & SEO polish

  • Fix canonical (use link, not meta; use https; full domain):
<link rel="canonical" href="https://www.loc.gov/">
  • og:type should be website for a homepage:
<meta property="og:type" content="website">
  • Add structured data with on-site search action:
<script type="application/ld+json">
{
  "@context":"https://schema.org",
  "@type":"WebSite",
  "name":"Library of Congress",
  "url":"https://www.loc.gov/",
  "potentialAction":{
    "@type":"SearchAction",
    "target":"https://www.loc.gov/search/?q={search_term_string}",
    "query-input":"required name=search_term_string"
  }
}
</script>
  • Resource hints for critical domains:
<link rel="preconnect" href="https://www.loc.gov" crossorigin>
<link rel="preconnect" href="https://cdn.loc.gov" crossorigin>
<link rel="preconnect" href="https://assets.adobedtm.com" crossorigin>
<link rel="preconnect" href="https://media.loc.gov" crossorigin>

4) Script loading & performance

You’re loading jQuery 1.8.2 (2012) synchronously and relying on .live() (deprecated since 1.9). Two safe options:

Option A (quick): keep versions, avoid blocking render

<script src="/static/js/lib/jquery-1.8.2.js" defer></script>
<!-- move inline jQuery code blocks *after* this script, also with defer -->
<script defer>jQuery(function($){ /* existing handlers */ });</script>

Why: defer queues parsing until after HTML, preserving execution order among deferred scripts, improving FCP/LCP.

Option B (better): upgrade to jQuery 3.x and replace .live() with .on()

Example conversions:

// BEFORE
$('.header-logo a').live('click', handler);
// AFTER
$(document).on('click', '.header-logo a', handler);

// BEFORE
$('.header-menu').live('hover', over, out);
// AFTER (hover shortcut preserved)
$('.header-menu').on('mouseenter', function(e){ over.call(this,e); })
                 .on('mouseleave', function(e){ out.call(this,e); });

(Do a global find for .live( across header, breadcrumbs, menu, search, footer bindings.)

Passive listeners (scroll/drag) for smoother scrolling

You can safely switch some to passive:

window.addEventListener('scroll', onScroll, {passive:true});
horizontalScrollingNavigation.addEventListener('scroll', onScroll, {passive:true});

5) Security hygiene

  • Add rel="noopener noreferrer" to every target="_blank":
<a href="https://library-of-congress-shop.myshopify.com/" target="_blank" rel="noopener noreferrer">Shop …</a>
  • Consider a Content-Security-Policy header (at least script/style nonces for inline blocks) on the server side. It will also help rein in third-party tags.
  • Use HTTPS everywhere (you still have a few http:///protocol-relative references in Open Graph & elsewhere).

6) Video player a11y & perf niceties

  • Add controlslist="nodownload" if desired and playsinline for mobile:
<video controls preload="metadata" playsinline controlslist="nodownload" …>
  • Poster already present (good). Keep captions (<track>)—great for a11y.
  • For users with reduced motion, the script above doesn’t auto-play; your player already requires user interaction to play, which is good.

7) Minor accessibility/content refinements

  • Ensure unique link text when repeating “Read more / Learn more” patterns—yours are already mostly descriptive; keep it that way.
  • Social icons already have alt—good. Make sure the visible label (e.g., title) matches what screen readers announce meaningfully.
  • The “Back to top” button already sets focus to #top—👍.

8) Fonts & CLS

  • You preload fonts (great). In your CSS, ensure font-display:swap; on the @font-face rules to avoid FOIT.
  • You’re setting width/height on most images and using aspect-ratio for tiles—good for CLS.

Paste-ready micro-patch bundle

Canonical + OG type

<link rel="canonical" href="https://www.loc.gov/">
<meta property="og:type" content="website">

Resource hints

<link rel="preconnect" href="https://www.loc.gov" crossorigin>
<link rel="preconnect" href="https://cdn.loc.gov" crossorigin>
<link rel="preconnect" href="https://assets.adobedtm.com" crossorigin>
<link rel="preconnect" href="https://media.loc.gov" crossorigin>

Hero preload

<link rel="preload" as="image"
      href="/static/home/images/featured/nbf/2025-natbookfest2_1200x560.jpg"
      fetchpriority="high">

Reduced motion + slider pause (from §1).

Safer external links (pattern):

<a href="https://newsroom.loc.gov/…" target="_blank" rel="noopener noreferrer">…</a>

If you’d like, I can provide a small PR-style diff (head block + aria labels + defer + reduced-motion script + external link rels) sized to this exact file so you can drop it in with minimal churn.