You can upload your logos and set your brand colours in order to make the CRM your own. These elements will be used in any public-facing interfaces (like shared forms or emails) and on your login screen.
Adding your branding to the CRM
Head to your Tools & Settings in the top right corner menu, then click Branding.
Within the Branding settings, you can add:
A main logo
An external logo, used on screens like your membership management portal or on externally shared record forms
An icon, used in browser tabs next to the name of the page
Your brand colours (you should refer to your organisation's brand guidelines for colour codes, or use a search engine)
Add in your branding, and hit save!