Stack columns on small screens.
Change a two-column CSS grid to one column at a viewport breakpoint.
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Example</title>
<style>
.grid { display:grid; grid-template-columns:1fr 1fr; } @media(max-width:600px) { .grid { grid-template-columns:1fr; } }
</style>
</head>
<body>
<div class="grid"><div>A</div><div>B</div></div>
</body>
</html>Expected output EXAMPLE
At a 1000 × 800 CSS-pixel viewport, unless another size is stated: At a 390-pixel viewport width, the grid items stack vertically. At 1000 pixels, they appear beside one another.
Details
Save this complete HTML example as example.html. The embedded CSS styles the fixture. Expected output describes the layout or computed style checked in Chromium.
Tested on Ubuntu 24.04.5 LTS · · Chromium 141.0.7390.37 · libc6 2.39-0ubuntu8.9; Playwright 1.56.0
Test inputs, results and environment
The exact published code ran in a dedicated Linux test container with prepared inputs. Unprivileged snippet process, external networking disabled, read-only root filesystem, and a fresh temporary working directory. Fixtures and output records are isolated from the application database. Testing covers this example and its stated checks, not every input, operating system, or runtime version. The Linux container shares its host's kernel; this is not a native Windows test.
- Architecture / host kernel
- x86_64 / 6.18.54.1-microsoft-standard-WSL2
- Snippet identity / locale
- uid=65534, gid=65534 (unprivileged) / C.UTF-8
- Interpreter invocation
Chromium: open example.html; execute the published browser assertions- Container image ID
sha256:32dc2d998158b6554c99b73b533f423696a0f3e31e8cbea9db10b5eee9a2fadd- Code SHA-256
8ffcbcc90dea338a2e8a0d73e52ca609ad3a3eddb04c523141c36cc4ece3ffe7- Dependencies
- libc6 2.39-0ubuntu8.9; Playwright 1.56.0
Test input setup
These are the prepared inputs used by the test harness. See Details above for the prerequisites and how to run this example.
# No input files required.
Observed standard output
Expected output describes the rendered page. The standard-output record below is the browser test harness receipt; the additional assertions check the result and interactions.
Stack columns on small screens: browser checks passed.
Exit code: 0. Standard error: empty. Validation: Shape/content assertions. System-dependent values above are one recorded run.
Additional assertions that passed
Checks recorded by the test harness. Where Python assertions are shown, browser cases use Playwright and simulator cases may inspect pin transitions: result.stdout is captured output, work is the temporary directory, and Path is pathlib.Path. The harness also imports json and csv.
await page.set_viewport_size({'width':390,'height':844})
a=await page.locator('.grid > div').nth(0).bounding_box(); b=await page.locator('.grid > div').nth(1).bounding_box()
assert b['y']>a['y']
await page.set_viewport_size({'width':1000,'height':800})
a=await page.locator('.grid > div').nth(0).bounding_box(); b=await page.locator('.grid > div').nth(1).bounding_box()
assert b['y']==a['y']