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<style>header { position: sticky; top: 0; }</style><main class="demo"><header>Example heading</header></main>
The useful mental model here is practical: how sticky offsets interact with scroll containers and how layered UI elements stay attached to useful boundaries. When a rule looks obvious but the browser produces something else, start by identifying which constraint or rendering phase is actually winning.
A good CSS change narrows the problem. Keep sticky elements inside a context whose scroll behavior you understand. Unintended overflow on a parent is a common cause of “sticky works on one page but not another.” This keeps the rule understandable when content, theme, or viewport conditions change later.
<style>.rail { position: sticky; inset-block-start: 1rem; }</style><main class="rail">Example content</main>
Engineering judgment: Keep sticky elements inside a context whose scroll behavior you understand. Unintended overflow on a parent is a common cause of “sticky works on one page but not another.”
| Concern | What to inspect | Typical failure |
|---|---|---|
| Core behavior | Sticky Positioning and Layered Interfaces | A sticky element can stop sticking when an ancestor creates the wrong scrolling context or when there is not enough scrollable room. Inspect the ancestor chain before blaming z-index. |
| Production test | Real content and constraints | The rule works only for the demo values |
| Maintenance | Scope and override path | A later fix creates another exception |
The useful mental model here is practical: how sticky offsets interact with scroll containers and how layered UI elements stay attached to useful boundaries. When a rule looks obvious but the browser produces something else, start by identifying which constraint or rendering phase is actually winning.
<style>.drawer { position: fixed; inset: auto 1rem 1rem; }</style><main class="drawer">Example content</main>
Layered panel is useful here because it demonstrates sticky positioning and layered interfaces under a concrete input rather than as an abstract property list.
<style>.content { overflow: auto; }</style><main class="content">Example content</main>
Scroll container is useful here because it demonstrates sticky positioning and layered interfaces under a concrete input rather than as an abstract property list.
Finish the lesson once you have worked through the material. This awards ★ 20 XP.