fix(image): use CSS styles for width/height to support percentage values#9966
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The ImageOutput component used HTML attributes for width/height, which only accept pixel values. This prevented percentage values like '100%' from working. Changed to use CSS styles instead of HTML attributes, which support both pixel values and percentage values. Fixes marimo-team#9810
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Pull request overview
Updates the frontend image output renderer so width/height can be expressed using CSS (supporting percentage values like "100%") instead of relying on <img> HTML attributes that effectively only work with pixel/integer sizing.
Changes:
- Broadened
ImageOutputprops to acceptnumber | stringforwidth/height. - Converted numeric dimensions to
"${n}px"and passed string dimensions through unchanged. - Switched from
<img width/height>attributes tostyle={{ width, height }}.
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| // Convert numeric values to pixel strings, pass string values (like "100%") as-is | ||
| const style: React.CSSProperties = {}; |
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| // Convert numeric values to pixel strings, pass string values (like "100%") as-is | ||
| const style: React.CSSProperties = {}; | ||
| if (width !== undefined) { | ||
| style.width = typeof width === "number" ? `${width}px` : width; | ||
| } | ||
| if (height !== undefined) { | ||
| style.height = typeof height === "number" ? `${height}px` : height; | ||
| } |
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| return ( | ||
| <span className={className}> | ||
| <img src={src} alt={alt} width={width} height={height} /> | ||
| <img src={src} alt={alt} style={style} /> | ||
| </span> | ||
| ); |
mscolnick
approved these changes
Jul 1, 2026
akshayka
added a commit
that referenced
this pull request
Jul 10, 2026
This PR changes images to carry their width and heights as HTML attributes instead of as inline styles. This in turn allows our stylesheet to correctly scale images when rendered in (for example) hstacks. String values like "100%" are only valid in CSS and still go through the style attribute, preserving the percentage support added in #9966. In particular, this prevents matplotlib figures (which carry pixel dimensions in their mimebundle metadata since #9144) from being squished or distorted. Before change: <img width="802" height="548" alt="image" src="https://github.com/user-attachments/assets/748c5568-6689-4896-988a-7eebe5022af2" /> With fix: <img width="722" height="382" alt="image" src="https://github.com/user-attachments/assets/e0e41052-7a71-4891-b869-ccc27341e6c9" />
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Summary
The ImageOutput component used HTML attributes for width/height, which only accept pixel values. This prevented percentage values like '100%' from working.
Motivation
Fixes #9810
Users reported that setting
height=100%on images and videos did not work.Changes
Validation
mo.image(src, height=100)still works (converted to "100px")mo.image(src, height="100%")now works correctlymo.image(src, width="50%")now works correctlyChecklist