How It Works

The sandbox renders a preview “canvas” with a scrollable area, a container box, and a movable element (the demo box). You choose a positioning mode and offsets (top/right/bottom/left), and the preview updates to show where the element lands. At the same time, the tool builds a ready-to-use CSS snippet that matches your settings, so you can paste the result into a component stylesheet or a CodePen and compare behavior.

To keep the experience realistic, the preview includes boundaries and optional guides. This makes it easier to answer the common questions that come up during layout work: “Which box is the reference for absolute positioning?”, “Why does sticky stop at a certain point?”, or “Why does z-index work in one place but not another?”

The generated snippet focuses on the core rules (position + offsets + z-index + sizes). It does not attempt to guess your entire layout system; instead, it gives you a minimal, dependable baseline that you can integrate into your own markup and utilities.

Step-by-step flow

• 1) Pick a position mode: static, relative, absolute, fixed, or sticky. Each one has different rules for flow, offsets, and scroll interaction.
• 2) Set offsets: add top/right/bottom/left values to see how each mode responds. Try entering only one side, then two sides, to understand constraint behavior.
• 3) Configure the container: toggle whether the container is positioned (position: relative), and adjust its size. This highlights how absolute positioning searches for a positioned ancestor.
• 4) Simulate scroll: adjust the scroll area height and test sticky behavior. The surrounding “content” blocks let you see when the element sticks and when it releases.
• 5) Review the CSS: copy or download the generated snippet and apply it in your layout. If your project uses utility classes, translate the snippet into utilities with confidence.

Because the preview is built from the same values used to generate the code, what you see is what you copy. This makes it practical both as a learning tool and as a debugging companion when a layout behaves unexpectedly. It is also helpful for documenting decisions: you can save a snippet that explains why a component uses absolute positioning rather than margin hacks or brittle transforms.

When you are testing sticky, pay attention to the scroll container. Sticky does not stick to the entire page unless the page itself is the scroll container. In many apps, an inner panel scrolls, and sticky elements are constrained by that panel. The sandbox is designed to make that boundary obvious.

Key Features

Visual preview with a realistic layout context

The sandbox includes a scroll wrapper, a container, and surrounding content spacing so you can test positioning the way it happens on real pages. This is especially helpful for sticky elements, which depend on scroll position and the boundaries of their scroll container. You can also test how large offsets behave when the container is smaller than you expect, which is a common source of “missing” elements.

To keep the preview readable, the container and demo box use clear borders and background contrast. Optional grid lines and guides help you reason about alignment and measure spacing visually without opening devtools.

Container “positioned or not” toggle

Absolute positioning is often misunderstood because its reference box changes based on the nearest positioned ancestor. With one switch you can set the container to position: relative (making it the containing block) or leave it unpositioned to illustrate how the element can jump to a different reference.

This is the exact scenario you run into with dropdown menus: a menu is absolutely positioned, but it unexpectedly aligns to the page rather than the card you intended. Toggling the container in the sandbox reproduces that behavior in a controlled environment, making it easier to spot the missing “position: relative” in your own markup.

Offset controls for all four edges

Enter any combination of top, right, bottom, and left values to explore how the browser resolves offsets. You can quickly see why specifying both left and right can stretch an element (when width is auto), or why certain offsets have no effect in static positioning. Try negative values to understand how elements can overlap or escape their container.

The tool also helps you build intuition about which offsets are “active” for each positioning mode. For example, relative offsets are applied after layout, while absolute offsets are applied during positioning relative to the containing block. The visual difference can be subtle in simple examples but becomes obvious when surrounding content is present.

Z-index and layering test

Use the z-index field to visualize stacking. The preview includes borders and optional guides so you can see which box is above the other, and the generated snippet reminds you when z-index only applies to positioned elements. If you have ever wondered why increasing z-index does not bring an element forward, you can use the sandbox to confirm that positioning and stacking contexts matter.

In real projects, overlays like modals and dropdowns often fail because they sit inside a component that forms a stacking context. While this sandbox keeps the environment simple, it still teaches the foundational rule: z-index compares elements within the same stacking context, and certain parent properties can isolate children from the rest of the page.

Copy and download the generated CSS

When you land on a configuration that matches your scenario, copy the CSS with one click or download it as a text file. This keeps the sandbox from being “just a demo” and turns it into a practical utility during development.

The output is intentionally minimal and readable. You can paste it into a component, translate it into utility classes, or use it as a checklist when reviewing a bug report: position mode, offsets, containing block, and layering are all captured in one place.

Use Cases

• Debugging a tooltip or dropdown: test absolute positioning inside a relatively positioned card, and verify how offsets behave when you change the container. This is ideal for menus that should align to a button, not to the page corner.
• Building fixed headers or floating action buttons: simulate fixed positioning relative to the viewport and confirm how it behaves as you scroll. Use different top/right values to check responsive anchoring patterns.
• Designing sticky sidebars: experiment with sticky top offsets and see exactly when the element sticks and when it stops at the scroll boundary. This mirrors common documentation layouts and dashboard side panels.
• Teaching CSS fundamentals: show students why static ignores offsets, why relative keeps the element’s original space, and why absolute is removed from the normal flow. The preview makes “normal flow” visible by preserving surrounding content.
• Layering UI components: test z-index changes and understand when stacking contexts can prevent an element from appearing on top. Use the sandbox as a quick preflight before you implement an overlay system.
• Comparing offset combinations: explore the difference between top/left vs bottom/right strategies and see how they interact with element size. This is useful for badges, corner ribbons, and notification dots.
• Reproducing a bug report: when someone says “the element jumps on scroll,” recreate the scroll container and positioning mode here first. A smaller reproduction helps you fix the real issue faster.
• Experimenting with negative offsets: test what happens when elements overlap or intentionally extend outside their container, such as decorative accents or hero section highlights.

Whether you are working on a production layout or learning positioning for the first time, the sandbox helps you connect CSS declarations to on-screen results. The goal is to reduce guesswork and make positioning predictable. Once you understand which reference box is used and how scroll boundaries apply, many “mystery bugs” become straightforward to solve.

Optimization Tips

Prefer layout primitives before positioning

Many “positioning problems” disappear when you use modern layout tools like Flexbox and Grid. Reach for absolute or fixed positioning when you truly need to remove an element from the normal flow or anchor it to a viewport edge. If your design is mostly about alignment and spacing, a layout container often produces cleaner, more responsive results.

As a rule of thumb, use positioning for overlays, anchored UI, or deliberate overlap. Use layout systems for structure. This separation keeps your CSS easier to reason about and reduces the chance that small content changes will break the design.

Use relative positioning sparingly for nudges

Relative positioning is great for small adjustments because it preserves the element’s original space. If you find yourself adding large relative offsets to make a layout work, consider whether your document flow needs a different structure. Large offsets can become brittle when content changes or when the layout adapts to mobile.

If you only need a one-off visual tweak, relative is fine. But if multiple components depend on offsets, you may be encoding layout assumptions in the wrong place. Try moving the alignment responsibility to a parent layout container instead.

Be mindful of stacking contexts

When z-index “does nothing,” it is often because a parent creates a new stacking context (for example via transforms, opacity changes, or a positioned element with z-index). Keep stacking simple by limiting the number of layers, and document your z-index scale so components don’t fight each other.

When building a design system, reserve ranges for common layers (base content, sticky headers, dropdowns, modals, toasts). This prevents ad-hoc z-index values from escalating over time and makes overlay behavior consistent across the app.