In modules/mod_cblogin/mod_cblogin.php find the places that display the things you want to tweak such as where the img src is being called for the avatar and so on. Unfortunately many of the things you need to tweak either have inline styling or the tags don't have an id or class at all so you'll need to give them a class. For example, where it says <img src="blablabla... you can change it to <img class="mynewclass" src="blablabla... and then in a css stylesheet you can add the css tweaks to size or whatever you want to change.
In your case if it were me I would just wrap the entire thing in it's own div wrapper such as <div class="cbloginwrapper"> and from that point you can do much of what you need to do without having to give each single tag a class or id by doing something like .cbloginwrapper img { max-width:25px; line-height: 2px; } which will change the max width of all images within the cb login module assuming of course you want them all to be the same size, and will change the line spacing for the entire module.
Remember that you'll need to remove all of the inline styling for a tag if you want to change it through a css stylesheet, the inline style will always take priority over what's in the css file. Inline styles are places in the php file that say style="whatever".
Using inline styles are a pretty big pet peeve of mine, it makes it time consuming and difficult to change simple things quickly. The only time I ever see a need for it is in some certain situations where you need to set the style through javascript.
