How to Customize the HTML Output Generated by export_to_html()?

[Aneesabegumj]

Hi Team,

I am converting Scanned/Readable PDFs to HTML using Docling. Here is the relevant part of my code:

pdf_opts = PdfFormatOption(
ocr=True,
dpi=300,
ocr_engine="rapidocr"
)

converter = DocumentConverter(
allowed_formats=[InputFormat.PDF],
format_options={InputFormat.PDF: pdf_opts}
)

result = converter.convert(pdf_path)
html_text = result.document.export_to_html()

The HTML output works, but it uses a default style/layout.

I want to understand:

1. How the HTML structure and styling are generated, and
2. Whether there is any way to customize the HTML design (custom CSS, templates, layout changes, removing default styling, etc.).

Is there any built-in support for customizing the HTML output?
Or should I post-process the generated HTML manually?

If you need any further details from my side, please feel free to contact me at: aneesa.j@fintags.in

[dosubot[bot]]

Hi @Aneesabegumj! I'm Dosu and I’m helping the docling team.

Docling’s export_to_html() generates HTML using a serializer that builds the structure (DOCTYPE, html, head, body) and applies default CSS for either a single-column or split-page layout. You can customize the output in several ways:

• To include or exclude headers/footers, use the included_content_layers parameter (e.g., included_content_layers={ContentLayer.BODY, ContentLayer.FURNITURE}) [source].
• To switch between single-column and split-page layouts, set split_page_view=True or False.
• To inject your own CSS (and override the default), pass a css_styles string to the HTMLParams object. If you want no styling, pass an empty style tag (css_styles="<style></style>") [source].
• To override the entire section, use the html_head parameter.

Example for custom CSS:

from docling_core.types.doc.document import ContentLayer
from docling_core.transforms.serializer.html import HTMLParams

custom_css = """
<style>
  body { background: #222; color: #eee; }
  /* your custom styles here */
</style>
"""

params = HTMLParams(
    css_styles=custom_css,
    layers={ContentLayer.BODY, ContentLayer.FURNITURE},
    output_style="single_column"
)
html = result.document.export_to_html(
    included_content_layers=params.layers,
    split_page_view=(params.output_style == "split_page"),
    html_head=None,  # or your own head HTML
    # ...other params as needed
)

There’s no built-in support for custom HTML templates or arbitrary layout changes beyond these parameters. For advanced customization (like changing the HTML structure), you’ll need to post-process the generated HTML [source].

To reply, just mention @dosu.

---

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[aonexyz]

Docling’s HTML output is mostly auto-generated from its internal document model, so the structure and styling are not meant to be highly customizable by default.

Here’s how it works:

1. HTML Structure
   The converter exports a block-based representation of the PDF.
   Each block is mapped to elements like <div>, <p>, <span>, etc.
   The layout is preserved to keep visual accuracy, so Docling inserts its own classes and inline styles.

2. Styling
   Docling uses minimal default styling (often inline) to keep formatting consistent with the PDF.
   There isn’t a built-in “theme” or “template” system.

3. Customization Options
   As of now, Docling does not provide:

   • custom CSS injection
   • custom HTML templates
   • layout overrides
   • removal of default inline styles

   The library focuses on accurate extraction, not on HTML theming.

4. What you can do
   If you want a different HTML layout/design, the recommended approach is:

   • Post-process the generated HTML
     Remove/replace inline styles, inject your own CSS, or reorganize the structure according to your needs.

   • Parse result.document
     Since the converter already gives you a structured document tree, you can write your own renderer to output custom HTML exactly the way you want.

5. In short

   • Docling - accurate extraction, fixed structure
   • You - apply custom styling or rebuild the HTML if you need full control

So yes, you can customize the output, but it requires manual post-processing or building a small custom HTML generator around result.document.

Hope this helps😊