In your account settings you can find the following settings:
Your Account settings can be found if you click on the wheel on the left top (see image below).
If you lost access to your current password you can reset your password with this link:
Your username is your unique identifier on Sitesights. You can log in with this username and you can see it under your profile with an @ like @johndoe.
Your current theme (dark or light) is preselected by your browser theme choice. You can change it anytime by clicking the button on the top right.