Lily Design System™

Aspect Ratio Container

An aspect ratio component is a layout utility that constrains its content to a specific width-to-height ratio. It ensures that images, videos, maps, and other embedded content maintain consistent proportions regardless of the container size. Common aspect ratios include 16:9 (widescreen video), 4:3 (traditional display), 1:1 (square, often for avatars or thumbnails), and 21:9 (ultrawide).

This component sets the CSS aspect-ratio property on a wrapper <div> element via an inline style, allowing consumers to control sizing through their own stylesheets while the component guarantees the proportional constraint.

Example

16:9
Show demo markup 
<div class="aspect-ratio-container" style="aspect-ratio:16/9;background:#e5e7eb;display:flex;align-items:center;justify-content:center;">16:9</div>
Usage example 
<script lang="ts">
  import AspectRatioContainer from './AspectRatioContainer.svelte';
</script>

<AspectRatioContainer ratio={16 / 9}>
  <video src="promo.mp4" controls></video>
</AspectRatioContainer>
Show Svelte source 
// In your Svelte component:
import AspectRatioContainer from "lily-design-system-svelte-headless/components/AspectRatioContainer/AspectRatioContainer.svelte";

<AspectRatioContainer>
  <!-- content -->
</AspectRatioContainer>

Usage

Widescreen video container:

<AspectRatioContainer ratio={16/9}>
  <video src="video.mp4" controls></video>
</AspectRatioContainer>

Square avatar container:

<AspectRatioContainer ratio={1}>
  <img src="avatar.jpg" alt="User avatar" style="object-fit: cover; width: 100%; height: 100%;" />
</AspectRatioContainer>

Embedded map with a 4:3 ratio:

<AspectRatioContainer ratio={4/3}>
  <iframe src="https://maps.example.com/embed?q=London" title="Map of London"></iframe>
</AspectRatioContainer>

Thumbnail grid with consistent proportions:

<div class="thumbnail-grid">
  <AspectRatioContainer ratio={3/2}>
    <Image src="photo-1.jpg" alt="Beach at sunrise" />
  </AspectRatioContainer>
  <AspectRatioContainer ratio={3/2}>
    <Image src="photo-2.jpg" alt="Mountain landscape" />
  </AspectRatioContainer>
  <AspectRatioContainer ratio={3/2}>
    <Image src="photo-3.jpg" alt="City skyline at night" />
  </AspectRatioContainer>
</div>

Props

  • ratio: number (default: 1) -- aspect ratio as width/height
  • children: slot (required) -- content to display within the container
  • ...restProps: Any additional HTML attributes passed to the <div> element

Keyboard Interactions

  • None -- this component is a passive layout container

ARIA

  • None -- transparent layout container; content within maintains its own accessibility semantics

When to Use

  • Use for constraining images, videos, maps, or embedded content to a consistent aspect ratio regardless of viewport size.
  • Use when you need responsive media containers that maintain proportional dimensions, such as 16:9 for video or 1:1 for avatars.
  • Use for thumbnail grids where all items must have uniform dimensions.
  • Use for embedded maps, iframes, or third-party widgets that need a fixed proportion.

When Not to Use

  • Do not use for text-only content where natural height should determine the layout.
  • Do not use when native image sizing is sufficient -- use Image with intrinsic dimensions instead.
  • Do not use for flexible containers that should adapt height to their content.

Headless

This component provides a <div> wrapper with the CSS aspect-ratio property set via inline style and a data-aspect-ratio attribute for consumer selectors, with zero visual styling. The consumer is responsible for all CSS including overflow behavior, border radius, background, and how child content fills or fits within the container.

Styles

The consumer provides all CSS styling. The component renders with a .aspect-ratio-container class for targeting. No default styles are included — this is a fully headless component.

Testing

  • Verify the component renders a <div> element with class aspect-ratio-container
  • Verify keyboard interactions work correctly
  • Verify pass-through attributes are applied

Advice

  • Designers: Choose standard aspect ratios (16:9, 4:3, 1:1, 21:9) for consistency across the interface. Ensure fallback behavior for content that cannot fill the container.
  • Developers: Use ratio={16/9} as a JavaScript expression rather than a string. Ensure child content uses object-fit or similar CSS to handle how it fills the container.

Implementation Notes

  • Pure layout utility -- no ARIA role needed
  • Uses inline aspect-ratio CSS property
  • data-aspect-ratio attribute exposed for consumer CSS selectors
  • Ratio prop is a number (width/height), e.g., 16/9 evaluates to 1.777...
  • Content is provided through child elements

Related components

  • container — a generic block-level content container
  • image — an image element with alt text

References

Canonical contract

Generated from this component's canonical metadata — the machine-checked source the implementations are held to.

Metadata

  • Component: aspect-ratio-container
  • PascalCase: AspectRatioContainer
  • Description: a container that maintains a fixed aspect ratio
  • Status: beta — implemented and unit-tested in all seven frameworks with an axe-clean demo page; not yet exercised in composed flows
  • HTML tag: <div>
  • CSS class: .aspect-ratio-container
  • Interactive: no

ARIA

  • None -- transparent layout container; content within maintains its own accessibility semantics

Keyboard

  • None -- this component is a passive layout container

Props

  • ratio: number (default: 1) -- aspect ratio as width/height
  • children: slot (required) -- content to display within the container
  • ...restProps: Any additional HTML attributes passed to the <div> element