require-theme-classic-custom-css-files-exist

Require statically configured Docusaurus classic-theme customCss paths to exist.

Targeted pattern scope

This rule focuses on docusaurus.config.* files.

It validates statically known classic-theme customCss entries from:

classic preset theme.customCss
direct @docusaurus/theme-classic options

What this rule reports

This rule reports customCss entries when the configured stylesheet path resolves to a file that does not exist.

Why this rule exists

customCss is meant to load real theme stylesheets.

A missing file path leaves the classic theme config looking complete while pointing at a stylesheet that cannot actually be loaded.

❌ Incorrect

export default {
    presets: [[
        "@docusaurus/preset-classic",
        {
            theme: { customCss: "./src/css/missing.css" },
        },
    ]],
};

✅ Correct

export default {
    presets: [[
        "@docusaurus/preset-classic",
        {
            theme: { customCss: "./src/css/custom.css" },
        },
    ]],
};

Behavior and migration notes

This rule is report-only.

It does not try to invent replacement stylesheet paths or remove missing entries automatically.

Additional examples

❌ Incorrect — one missing entry inside a `customCss` array

export default {
    themes: [[
        "@docusaurus/theme-classic",
        {
            customCss: [
                require.resolve("./src/css/custom.css"),
                "./src/css/missing.css",
            ],
        },
    ]],
};

✅ Correct — only existing stylesheet paths

export default {
    themes: [[
        "@docusaurus/theme-classic",
        {
            customCss: [require.resolve("./src/css/custom.css")],
        },
    ]],
};

ESLint flat config example

import docusaurus2 from "eslint-plugin-docusaurus-2";

export default [docusaurus2.configs.recommended];

When not to use it

Do not use this rule if your project intentionally keeps unresolved placeholder stylesheet paths in config and you do not want linting to report them yet.

Rule catalog ID: R098

Targeted pattern scope​

What this rule reports​

Why this rule exists​

❌ Incorrect​

✅ Correct​

Behavior and migration notes​

Additional examples​

❌ Incorrect — one missing entry inside a customCss array​

✅ Correct — only existing stylesheet paths​

ESLint flat config example​

When not to use it​

Further reading​