Before this lesson
Understand the box model, overflow, positioning and document flow.
What you will be able to do
Identify sticky and overflow causes instead of hiding clipped content.
Understand the mechanism
Overflow controls excess content and can establish scrolling behavior that changes sticky positioning. Map ancestor sizes and overflow values before diagnosing the result; the effect extends beyond clipping.
Sticky participates in normal flow and then responds to an inset while scrolling. It needs room to move; short containers or no scrolling can hide the effect. A top inset does not make it permanently fixed to the viewport.
Trace horizontal overflow to actual bounds: long tokens, fixed images, minimum grid tracks or flex sizing. Code blocks can scroll locally while prose wraps. Hiding root overflow can conceal controls and focus rather than fixing the cause.
Give overlapping sticky headers explicit backgrounds and stacking behavior. Check focused links and anchors are not obscured; scroll-margin-top can account for headers when appropriate.
Runnable example
Run HTML examples as separate .html files in a modern browser. Prepare resource files and multi-file modules as described in the lesson.
<!doctype html>
<html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width,initial-scale=1"><title>Honeysuck practice</title></head><body>
<style>
.panel{height:260px;overflow:auto;border:1px solid #bdcdbf;max-width:600px}
.panel h2{position:sticky;top:0;margin:0;padding:12px;background:#e9f2e4;z-index:1}
.panel p{padding:16px;min-height:150px;margin:0;border-bottom:1px solid #ddd}
.panel a{scroll-margin-top:70px}
</style><section class="panel" tabindex="0" aria-label="Scrollable lessons"><h2>Course notes</h2><p>First note. Scroll inside this panel.</p><p>Second note with more reading.</p><p><a id="last" href="#last">Last note</a></p></section>
</body></html>Trace and verify
Scroll the panel itself and watch the heading remain at its top. Remove the height and observe how scrollability changes; separately try visible overflow. Change one condition at a time and restore before comparing.
Common mistakes and boundaries
Arbitrary z-index values do not fix the wrong scroll ancestor. Fixed positioning is not interchangeable with sticky because it removes the element from normal flow.
Practice challenge
Add a long URL and code block: prose wraps, code scrolls locally, and the page itself does not overflow.
Reference solution and reasoning
Wrap prose and constrain pre with local overflow. Fix parent minimum-size constraints before adding scrolling for content that genuinely should not wrap.