.avatar-none is the CSS in UBB.threads 7.7.x
Control Panel > Styles > Edit or Add a Style > Misc. Properties > .avatar-nonehttps://www.ubbcentral.com/forums/u...e-ubb-threads-7-7-0-changelog#Post262031
[NEW] CP: Style Editor now allows styling of the Member Avatars. If you choose to use it, this property could be to set a border (solid, dashed, double, etc), the border size, and/or adjusting the border-radius for circular or just rounded corners for Member Avatars. This feature uses .avatar for members with avatars, and .avatar-none for members without avatars. When unset, the forum default avatars will not use borders, and will have a radius of 5px for all avatars.
Prior to that it was just this:
Control Panel > Profile Settings > Avatar Image Max Height/Width
Both use the same sizes as the rest of your user avatars