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Extracting the configured custom CSS for a tenant

Follow these steps to find the styling web address (the customcss link) that a company configured on its Microsoft sign-in page. Once you have it, check it with the Sign-in Page Branding Checker.

Prerequisite: you must have a Global Administrator or Branding Administrator role in the tenant you want to inspect.
1

Open Microsoft Graph Explorer

Go to Graph Explorer — Try Microsoft Graph APIs.

2

Sign in to your tenant

Use the Sign in button in the top-right corner and sign in with your admin account.

Signing in to Microsoft Graph Explorer using the Sign in button in the top-right corner.
Sign in from the top-right of Graph Explorer.
3

Get your Tenant ID

Send a GET request to the organization resource, then copy the id value from the response — that is your Tenant ID.

GET https://graph.microsoft.com/v1.0/organization
GET request to the organization resource; the id field in the response is the Tenant ID.
The id in the response is the Tenant ID.
4

List the configured branding locales

Send a GET request to the branding localizations resource (replace <tenantId> with the ID from step 3). The response has a value array — each item is a locale you configured.

GET https://graph.microsoft.com/v1.0/organization/<tenantId>/branding/localizations
GET request to the branding localizations resource returning a value array of locales.
The value array holds one entry per configured locale.
A locale entry showing the cdnList array and the customCSSRelativeUrl property.
Each locale exposes cdnList and customCSSRelativeUrl.
5

Build the custom CSS URL

For every locale that has custom CSS, the customCSSRelativeUrl property has a value (it is null when there is no custom CSS). Combine it with any value from the cdnList array to form the URL:

https://<value from cdnList>/<value from customCSSRelativeUrl>

Example from the sample tenant:

https://aadcdn.msftauthimages.net/dbd5a2dd-0weq2zut5agzo6joxgyyjtglszcozunpniz5gefzsrm/logintenantbranding/1033/customcss?ts=639195266646997629
6

Repeat for every configured locale

Repeat step 5 for each locale that has a custom CSS configured.

Shortcut: you don't have to build a URL for every locale by hand. Copy the full JSON response from step 4 and paste it into the Don't have the styling link? box on the checker — it builds every URL and checks all locales for you.