The best way to apply branding to a Salesforce org using Lightning Experience is to create a custom theme in Themes and Branding. Themes and Branding is a feature that allows the administrator to customize the look and feel of Salesforce to match the branding of the organization. The administrator can add logos, default images, and colors to the theme. The administrator can also choose one of the built-in Salesforce themes, or create their own custom themes with just a few clicks. To create a custom theme, from Setup, enter Themes and Branding in the Quick Find box, then select Themes and Branding. Click New Theme and upload the logo, brand colors, and images that follow the company design guidelines.The administrator can also preview and activate the theme for the entire org1.Reference:[Brand Your Org in Lightning Experience] (https://help.salesforce.com/s/articleView?id=sf.brand_your_org_in_lightning_experience.htm&language=en_US&type=5)