Cross-link CSS Containment piece

Author: csswizardry

_includes/footer.html

@@ -11,6 +11,7 @@ <h4 class=band__title>Learn:</h4>
       <li><a href="/2023/07/in-defence-of-domcontentloaded/">Does <code>DOMContentLoaded</code> Still Matter?</a>
       <li><a href="/2024/12/a-layered-approach-to-speculation-rules/">Push Speculation Rules to the Max</a>
       <li><a href="/2021/02/measuring-network-performance-in-mobile-safari/">Improve Web Performance on iOS</a>
+      <li><a href="/2026/04/what-is-css-containment-and-how-can-i-use-it/">Master CSS Containment</a>
       <li><a href="/max-age/"><code>max-age</code> calculator</a>
       <li><a href="/workshops/core-web-vitals-on-ios/">Core Web Vitals on iOS</a>
       <li><a href="/2024/09/optimising-for-high-latency-environments/">Design for High Latency</a>