Hi, There are 2 work arounds :
1. Make that "call code" on mod_relateditems_xtd.php commented out, so the module won't call the css file anymore.
2. If you don't want to modify the core file (suggestion no .1) then you can make the new css files has a stronger power by using more deep selector or by adding
!important in the end of css property.
For example :
original style :
.ac.image-border-light .image-feat img { padding: 3px; margin: 0; border: 1px solid #eee; }
you can make code like this to override that code :
#your-template-region .ac.image-border-light .image-feat img { padding: 10px; margin: 0; border: 5px solid #ffff00; }
or this one :
.ac.image-border-light .image-feat img { padding: 10px!important; margin: 0; border: 5px solid #ffff00!important; }
Have a try