Do these 3 things before closing this tab:
1Fix the driver behind crashes, sound loss and screen glitches2Repair Windows errors before they cause bigger problems3Scan for outdated or missing drivers - takes under a minuteWith Grover, pass your CSS string as the content of a style tag: style_tag_options: [{ content: css_string }]. Grover inserts that text into the HTML before Chromium renders the PDF, so you do not need to write a temporary stylesheet file.
Pass a CSS string to Grover
Grover’s documented inline-HTML API accepts style-tag options. The content value is the CSS text you want Chromium to apply.
require "grover"
css = <<~CSS
@page {
size: A4;
margin: 18mm;
}
body {
color: #222;
font-family: Arial, sans-serif;
font-size: 12pt;
}
h1 {
color: #b3261e;
page-break-after: avoid;
}
.notice {
background: #fff3cd;
border: 1px solid #e0b400;
padding: 12px;
}
CSS
html = <<~HTML
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Invoice</title>
</head>
<body>
<h1>Invoice 1007</h1>
<p class="notice">Payment received.</p>
</body>
</html>
HTML
pdf = Grover.new(
html,
style_tag_options: [{ content: css }]
).to_pdf
File.binwrite("invoice.pdf", pdf)This uses the same form shown in the Grover README: style_tag_options: [{ content: css_string }]. The result of to_pdf is binary PDF data, so write it with File.binwrite.
Why a CSS string is useful
Keeping CSS in a Ruby variable is practical when styles are generated from data, selected by a theme, or stored in a database or configuration service. It also avoids creating and cleaning up a temporary file for every job. The important distinction is between supplying CSS text and loading a stylesheet file: Grover’s content option is for text; url and path options are for separately stored stylesheets.
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Make the HTML and CSS deterministic
Keep the style text separate
Build the HTML and CSS independently, then pass both to Grover. This makes it easier to test the generated markup and to swap themes without concatenating unescaped fragments into the document.
Escape data inserted into HTML
CSS injection and malformed markup are separate concerns from PDF rendering. Escape user-controlled values before putting them in HTML, and validate any value that is interpolated into CSS (for example, a color or a length). Do not treat a CSS string as a safe place to interpolate arbitrary input.
Use print-aware CSS
Chromium renders a print document, not an interactive browser window. Put page rules in @page, avoid relying on hover states, and use page-break properties where a heading or table row must stay together. Confirm the output with the same Chromium environment used in production.
Loading a stylesheet file instead of a string in Grover
If your CSS already lives in a file or at a URL, use Grover’s documented path or url stylesheet options instead of reading it into a string solely to pass it as content. Relative references are a common source of missing styles. For direct conversions, Grover documents using a display_url or absolute paths; without a usable base, Chromium resolves relative paths against its default display URL, http://example.com.
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pdf = Grover.new(
html,
display_url: "https://app.example.test",
style_tag_options: [
{ path: "/absolute/path/to/print.css" }
]
).to_pdfThe exact option names and examples are maintained in the Grover README. Use a filesystem path that the rendering process can read, or a URL reachable from the machine running Chromium.
Using PDFKit when your CSS is already a string
PDFKit’s README documents creating a kit from HTML and adding stylesheet file paths with kit.stylesheets << '/path/to/css/file'. It does not document a dedicated CSS-string parameter. The straightforward HTML-level solution is to put the string inside a <style> element before passing the HTML to PDFKit.
require "pdfkit"
css = ".body { background: #f4f4f4; color: #222; }"
html = <<~HTML
<!doctype html>
<html>
<head>
<style>#{css}</style>
</head>
<body class="body">
<h1>Report</h1>
</body>
</html>
HTML
kit = PDFKit.new(html)
File.binwrite("report.pdf", kit.to_pdf)For linked CSS, PDFKit advises complete paths for images, stylesheets, and JavaScript in raw HTML. Its root_url and protocol options can provide a base for relative references. See the PDFKit README for the supported configuration.
Using Wicked PDF
Wicked PDF wraps wkhtmltopdf and is commonly used from Rails. Its README recommends absolute references for linked CSS and other assets because the executable runs outside the Rails application context. In Rails views, use the project’s stylesheet helpers; for an asset that must be embedded, the README documents wicked_pdf_asset_base64.
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Wicked PDF does not document a dedicated CSS-string parameter. For plain CSS text, insert a <style> element in the rendered HTML:
<style>
<%= @css_string %>
</style>Ensure the value is trusted or safely handled before placing it in a template. In production, precompile assets used by PDF views and verify that the generated URLs are absolute and reachable. The Rails-specific asset guidance is in the Wicked PDF README.
Why Prawn is a different choice
Prawn is a pure Ruby PDF generator, not an HTML-to-PDF renderer. Its README says it is not an HTML-to-PDF generator and that its limited inline styling is not intended for rich HTML. If your source is an HTML document and you need browser-like CSS, use an HTML renderer such as Grover, PDFKit, or Wicked PDF. Choose Prawn when you want to construct the PDF directly with Ruby drawing and layout primitives.
Choosing the renderer
| Renderer | CSS string support documented? | External-resource behavior | Typical use |
|---|---|---|---|
| Grover | Yes: style_tag_options: [{ content: css_string }] |
Use a display_url or absolute paths when relative paths cannot be resolved |
Chromium-based HTML and CSS to PDF |
| PDFKit | No dedicated option shown; put CSS in a <style> element |
Use complete paths, or configure root_url and protocol |
HTML passed to the PDFKit/wkhtmltopdf pipeline |
| Wicked PDF | No dedicated option shown; put CSS in rendered HTML | Prefer absolute references; precompile Rails PDF assets | Rails-oriented wkhtmltopdf integration |
| Prawn | Not an HTML-to-PDF path | You place content with Ruby APIs rather than loading an HTML stylesheet | Programmatic PDF generation |
The project documentation establishes these configuration differences, but it does not establish a controlled rendering-fidelity or performance benchmark. Select the engine whose HTML, CSS, asset, and deployment requirements match your application.
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Debugging missing CSS in the PDF
The CSS string is present but has no effect
- Confirm that the option is nested exactly as
style_tag_options: [{ content: css_string }]in Grover. - Check for invalid CSS by rendering a deliberately obvious rule such as
body { background: red; }. - Inspect generated HTML for an accidental escaped style tag or a missing closing tag.
- Check selector specificity and print rules. A later rule, an inline style, or a print stylesheet can override the declaration.
Linked styles or images disappear
- Replace relative URLs with absolute URLs or configure Grover’s
display_url. - For PDFKit, set an appropriate
root_urlandprotocol, or use complete paths. - For Wicked PDF, verify absolute asset references and production precompilation.
- Make sure the worker running the renderer can reach the host and read the files; your web browser’s access is not evidence that the renderer has the same access.
The PDF job hangs or fails
- Check that the renderer’s executable and Chromium or wkhtmltopdf dependency are installed in the worker environment.
- Remove network-dependent assets temporarily to identify a blocked request or unreachable host.
- Log the final HTML, CSS length, resource URLs, and renderer error output (without logging secrets such as authorization headers).
- Use a fixed timeout at the job layer and retry only failures that are safe to repeat.
Pagination differs between development and production
- Use the same renderer version, fonts, locale, and timezone in both environments.
- Embed or install the fonts your layout requires and avoid relying on a developer laptop’s font set.
- Set page size and margins explicitly with
@pageor the renderer’s PDF options.
Performance, reliability, and cost considerations
Inline CSS avoids a file lookup, but the expensive work is still browser startup, HTML layout, font loading, image decoding, and PDF serialization. Reuse a long-lived browser process where your chosen integration supports it, keep CSS and HTML no larger than necessary, and avoid waiting for third-party resources that are not needed in the document.
For repeatable jobs, cache stable assets, pin the runtime image, and record the renderer configuration with the generated document. A cache can improve latency, but it must be invalidated when CSS, HTML, fonts, or data change. None of the cited project documentation supplies a universal throughput, fidelity, or cost benchmark, so measure with your own documents and deployment.
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curl -G "https://api.screenshotneo.com/v1/shot"
-d access_key=YOUR_API_KEY
--data-urlencode url=https://example.com
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FAQ
Can I pass several CSS strings to Grover?
Yes. Supply multiple style-tag option hashes, each with its own content, or combine trusted rules into one string before calling Grover.new.
Should I inline CSS for every PDF?
Not necessarily. Inline text is convenient for generated or theme-specific rules. A versioned stylesheet file is easier to share across documents, provided the renderer can resolve its path or URL.
Does Prawn accept an HTML document and its stylesheet?
No. Prawn’s documented purpose is direct PDF construction in Ruby, not browser-style HTML and CSS rendering.
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Can I pass several CSS strings to Grover?
Yes. Supply multiple style-tag option hashes, each with its own content, or combine trusted rules into one string before calling Grover.new.
Should I inline CSS for every PDF?
Not necessarily. Inline text is convenient for generated or theme-specific rules. A versioned stylesheet file is easier to share across documents, provided the renderer can resolve its path or URL.
Does Prawn accept an HTML document and its stylesheet?
No. Prawn’s documented purpose is direct PDF construction in Ruby, not browser-style HTML and CSS rendering.
The Bottom Line
For Grover, the direct solution is style_tag_options: [{ content: css_string }]. Use absolute or explicitly rooted resource paths, and choose PDFKit, Wicked PDF, or Prawn only when its rendering model fits your input.
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