20 MB CSS sample

A CSS file of exactly 20,971,520 bytes. It is a valid Cascading Style Sheets file, generated by this site. Compare its checksum and test it with the parser used by your application. Use it wherever you need a 20 MB sample, test or dummy CSS file.

sample-css-20mb.css

20 MB20,971,520 bytes

Download 20 MB CSS

Created in your browser in a few seconds, then checked against the SHA-256 checksum. The file is not uploaded anywhere. No sign-up.

Type: text/css
SHA-256: 4cec96123c62049ab0d88cd120f2473916866b3d09f0859577a4b68772345e14
Delivery: Created in your browser from static generator assets (how it works).

What is in this file

A custom property block, a body rule and 210,128 class rules with colours, margins, padding and border radii. A comment at the end brings the file to the exact size.

Rules	210,130
Custom properties	2
Imports	None
Encoding	UTF-8 (ASCII characters only)

How the file begins

The opening lines of sample-css-20mb.css, exactly as they appear in the file.

00000000  2f 2a 20 53 61 6d 70 6c  65 54 65 73 74 46 69 6c |/* SampleTestFil|
00000010  65 73 20 73 61 6d 70 6c  65 20 43 53 53 20 66 69 |es sample CSS fi|
00000020  6c 65 20 28 32 30 20 4d  42 29 20 2a 2f 0a 3a 72 |le (20 MB) */.:r|
00000030  6f 6f 74 20 7b 0a 20 20  2d 2d 69 6e 6b 3a 20 23 |oot {.  --ink: #|

Preview

Creates the file in your browser and shows the first 64 KB of it.

Where 20 MB matters

A 20,971,520-byte file: right at the default attachment limit of Outlook, and just under the 25 MB ceilings of Gmail and GitHub web uploads. These are the default limits a file of this size is useful for testing:

System	Limit	Note
Microsoft Outlook	20 MB of attachments by default for internet mail accounts	This file is right at the limit; add a second attachment and it is exceeded.
Gmail	25 MB per message	Under the limit, although email encoding adds about a third in transit.
GitHub web uploads	25 MiB per file added through the browser	Accepted. Pushing with Git allows larger files.
Cloudflare Pages assets	25 MiB per file	The largest round size that can be served as a static asset.
Amazon API Gateway	10 MB payload	Rejected; the upload has to go directly to object storage.
ASP.NET Core (Kestrel)	About 28.6 MB request body by default	Accepted with room for the multipart overhead.

All 20 MB sample files

Use this file for

Finding the first upload limit in a new stack
Testing code editors and syntax highlighters
Testing minifiers and bundlers

Testing notes for CSS

With X-Content-Type-Options: nosniff, browsers refuse a stylesheet that is not served as text/css.

CSS format reference

Technical details

File name	sample-css-20mb.css
Format	CSS (Cascading Style Sheets)
Extension	.css
MIME type	text/css
Size	20,971,520 bytes (20 MB)
Kind	Text
SHA-256	4cec96123c62049ab0d88cd120f2473916866b3d09f0859577a4b68772345e14
Created	2026-10-23
Validation	See the listed size and SHA-256. Small downloads are checked in the browser; verify streamed downloads manually. A hash match does not prove parser compatibility.
Preview	Available on this page
Source	Generated in your browser by this site's generator; not copied from elsewhere
Licence	Free to use, modify and redistribute (terms)
Category	Code

Check the stated structure and checksum against your application requirements. As with any download, scan the file with your own security tools before opening it. How files are made and checked

Verify your copy

This file is created in your browser, so it has no direct URL for curl or wget. The generator is designed to produce reproducible bytes. After saving, compare the checksum with the SHA-256 value above.

sha256sum sample-css-20mb.css     # Linux
shasum -a 256 sample-css-20mb.css # macOS

On Windows, run Get-FileHash sample-css-20mb.css -Algorithm SHA256 in PowerShell. For scripts and pipelines, save the file once and keep your own copy.

Related files

Questions about this file

Is this file exactly 20 MB?: Yes. It is 20,971,520 bytes, which is 20 MB in the binary units that operating systems and server limits use (1 KB = 1,024 bytes).
What is inside the 20 MB CSS file?: A custom property block, a body rule and 210,128 class rules with colours, margins, padding and border radii. A comment at the end brings the file to the exact size.
What do the sample stylesheets contain?: Custom properties, a body rule and a long list of class rules, with no @import rules or external URLs.

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