CSS Triangle & Arrow Generator

Create lightweight, pixel-perfect directional arrows for tooltips, speech bubbles, and dropdown menus using the classic CSS border hack. No images or SVG files required.

How to Generate a Pure CSS Triangle

Generating standard geometric shapes without relying on heavy external images is a foundational skill in frontend development. Here is how to use our generator to craft the perfect directional arrow for your user interface:

Select the Direction: Use the 3×3 grid pad to choose where your arrow will point. Selecting a standard axis (Up, Down, Left, Right) creates an equilateral or isosceles triangle, while selecting a corner generates a right-angle triangle.
Adjust the Dimensions: Use the Width and Height sliders. For a standard tooltip pointing upwards, a width of 20px and a height of 10px provides a perfectly balanced, wide base.
Match Your Brand Color: Input the exact hex code of the parent container (like a tooltip bubble) so the arrow blends seamlessly into the design.
Export the Code: Click “Copy CSS”. Apply this code block to an empty div or, ideally, to a pseudo-element like ::before or ::after attached to your target component.

Technical Deep Dive: The Famous “Border Hack”

You might notice that the generated CSS code contains width: 0; and height: 0;. How does a box with zero dimensions display a colored shape? The secret lies in how web browsers render thick CSS borders.

Understanding Border Intersections

When you apply a thick border to a standard HTML div, the browser doesn’t draw straight lines connecting the edges. Instead, where the top border meets the right border, the browser draws an angled, 45-degree mitered corner to join them seamlessly.

If you shrink the width and height of the div to exactly zero, the inner space collapses. All that is left are the four thick borders converging on a single central point. These four borders now appear as four distinct triangles pointing toward the center.

Exploiting Transparency

To create a single directional arrow, we exploit the transparent CSS color value. By setting three of the four border triangles to transparent, and giving the fourth border a solid color, we isolate a single, perfect triangle. The direction the triangle points is simply dictated by which borders are left transparent.

Developer Use Cases for CSS Arrows

While newer techniques like clip-path exist, the classic CSS border hack remains the most universally supported, stable, and lightweight method for generating arrows.

1. Tooltips and Popovers

When a user hovers over a crucial UI element (like an “info” icon), a tooltip bubble appears. To visually connect the floating bubble to the icon, developers attach a small CSS triangle to the bottom of the tooltip, pointing directly at the icon. This clarifies the relationship between the UI elements instantly.

2. Breadcrumb Navigation

Complex web applications often feature breadcrumb navigation (e.g., Home > Settings > Profile). By utilizing right-pointing CSS triangles attached to the ::after pseudo-element of each breadcrumb link, you can create a continuous, interlocking ribbon effect that guides the user’s eye across the navigation path.

3. Chat and Speech Bubbles

Designing a messaging interface (like iMessage or WhatsApp) requires speech bubbles with small directional “tails” indicating who is speaking. A left-pointing CSS triangle attached to a message visually dictates that the message originated from the other user, while a right-pointing triangle indicates a message sent by the active user.

Performance: CSS Hack vs. SVG Icons

Why use this obscure border hack instead of simply importing an SVG icon of a triangle? The answer comes down to performance, network overhead, and DOM management.

Zero HTTP Requests: Loading an external SVG or PNG file requires a network round-trip. This CSS hack renders instantly as part of your initial stylesheet payload, protecting your Core Web Vitals.
Dynamic Color Matching: If you use an SVG, changing the tooltip color on hover or supporting Dark Mode requires loading a separate SVG or using complex inline SVG fills. With the CSS border hack, you simply target the border-color property in a media query, and it repaints instantly.
Reduced DOM Clutter: By applying this hack to a ::before pseudo-element, you generate the triangle without adding extra HTML tags to your document structure, keeping your markup semantically clean and accessible to screen readers.

Explore More Free CSS Generators

Return to our CSS Tools Hub to access our full collection of client-side developer utilities designed to streamline your frontend workflow.

Frequently Asked Questions

Is the CSS border triangle hack supported in all browsers?

Yes. Because this technique relies on the most fundamental CSS border rendering rules, it is universally supported across every single web browser in existence, including ancient legacy browsers like IE6. It is arguably the most stable UI hack in web development.

How do I attach this triangle to an existing div?

The best practice is to assign the generated CSS code to a pseudo-element (either ::before or ::after). Set the parent div to position: relative;, and set the pseudo-element to position: absolute;. This allows you to position the arrow cleanly along the outside edge of the parent container.

Why is the output code using decimal pixels?

When you create an arrow that points left or right, the browser calculates the opposite vertical borders based on half of your specified height. If you input an odd number for height (like 25px), dividing it by two results in 12.5px. Modern browsers render sub-pixel values perfectly through anti-aliasing.