JPG, PNG, GIF images will be scaled to fit 200 x 48 pixels. For SVG images, they will be resized to fit 24 pixels vertically. Your default logo can be in the JPG, PNG, GIF, or SVG format. For default theme, you also have an option to upload a logo image that is less than 10kb. Add a HTTPS image url that allows anonymous access and doesn't require authentication. Default logo: Add a URL location that points to your logo.On the Logos page, you can add your logos, and specify the URL where users will navigate to when they select the logo. You can also prevent users from overriding their theme and show the user's display name.
Under Groups, you can select up to 5 Microsoft 365 Groups that can see your group theme, instead of using the default theme. On the General page, enter a name for your new theme.
You can create up to four additional group themes. To delete the default theme, you have to delete all other themes first. The default theme is unique, it can't be renamed and applies to everyone within your organization.
You can add or update a default theme that applies to everyone within your org. The organization theme is what appears in the top navigation bar for people in your organization. As the admin of your organization, you can create multiple themes for the people in your organization, and select which themes apply to different members of your organization.