# My HTML Report Lost Its CSS — The Five Causes, In Order

Canonical: https://commareports.com/html-report-broken-css
Published: 2026-08-25

> An HTML report that renders as unstyled text or an empty page almost always fails for one of five reasons. How to tell which one, the fix for each, and how to stop it recurring.

# My HTML report lost its CSS

Unstyled text, a blank page, or a chart-shaped hole. Five causes, in
roughly the order they occur. The browser console names the one you have
— open it first.

## 1. Only the entry file travelled

Most tools that emit "an HTML report" emit a directory:
`index.html` plus `report_files/`, `assets/`, `jacoco-resources/`,
`_static/` — the naming varies, the shape doesn't. Copy the `.html` out
of it and every stylesheet and script reference points at nothing.

**Console says:** 404s on `.css` and `.js`.

**Fix:** move the whole directory, or publish the whole directory. If
the tool has a self-contained mode, use it — `nbconvert --embed-images`,
Altair's `inline=True`, Extent's offline mode, Plotly's
`include_plotlyjs=True`.

## 2. It's being opened from `file://`

A local page has an opaque origin. Module scripts (`<script
type="module">`) and `fetch`/`XMLHttpRequest` to sibling files are
blocked by the same-origin rules — deliberately, and with no flag worth
setting. Reports that load results as JSON (Vitest, several coverage
UIs) can't work this way at all; their own docs tell you to run a local
server first.

**Console says:** a CORS error on a module, or
`Cross origin requests are only supported for protocol schemes: http, https…`

**Fix:** serve it over HTTP. `python -m http.server` proves the
diagnosis; a published URL fixes it for everyone rather than for you.

## 3. A Content-Security-Policy is refusing the subresources

CI artifact viewers commonly serve artifacts under a strict CSP, which
is why the same file looks perfect locally and naked in the browser.
Jenkins is the best-known example — see
[the Jenkins CSP fix](/ci/jenkins-html-report) — and GitLab's and Azure's
artifact viewers have their own constraints.

**Console says:** `Refused to load the stylesheet…` or
`Refused to execute inline script…` because it violates the CSP.

**Fix:** stop relying on the artifact viewer as a rendering surface. It
is a file store that happens to return `text/html`.

## 4. The report was pasted somewhere that isn't a browser

Email clients strip `<script>` and external stylesheets, and Outlook on
Windows renders with the Word engine — no flexbox, no grid. Chat
clients preview markup as text. See
[emailing an HTML report](/email-html-report).

**Fix:** send a link, not markup.

## 5. It needs the network, and the network isn't there

A report that loads its libraries from a CDN renders as a skeleton on a
locked-down laptop, on a plane, or inside an air-gapped environment.

**Fix:** generate the self-contained variant when the audience might be
offline. When they're online, CDN-loaded reports are fine — subresources
fetched inside Comma's sandboxed frame aren't governed by the app's CSP,
and the common visualization CDNs (jsDelivr, unpkg, cdnjs, esm.sh) are
allow-listed anyway.

## Making it not happen again

Publish the output directory once and share the URL:

- `index.html` becomes the report body.
- The CSS, JS, JSON and images upload alongside it, and their relative
  references are rewritten to the uploaded copies. That single step
  removes causes 1, 2 and 3.
- Scripts run inside a sandboxed iframe (`allow-scripts`, no
  `allow-same-origin`), so interactivity survives —
  [interactive HTML reports](/interactive-html-reports).

Drag the folder (or a zip of it) into
[the app](https://commareports.com/), or publish it
[from CI](/docs/ci) so the fixed version is the one everyone gets.

**Limits:** entry HTML 5 MB; assets 25 MB per file, 250 MB and 500 files
per report.

## Try it

Comma is free — unlimited reports, unlimited commenters, unlimited
revision history.

**[Publish the whole report folder →](https://commareports.com/)**

### Related

- [Someone sent me an HTML file](/open-html-file-online)
- [Jenkins HTML report with no CSS](/ci/jenkins-html-report)
- [Interactive HTML reports](/interactive-html-reports) · [Publish from CI](/docs/ci)