Hi
Thanks a lot for your quick reply, I follow the same step as you mention but in line 718 there is nothing related to color! that what I found into assets\css\style.css (line 718):
.attach-file.change-card-attachment {
width: 100%;
-webkit-box-pack: start;
-ms-flex-pack: start;
justify-content: flex-start;
height: 32px;
cursor: pointer;
}