Well, let’s start with your login box, and see if we can get it working on just that one… then the process will be the same for others.
If you use firebug, and inspect your login widget, you will see it has an id of wp_sidebarlogin-6
. So, we would need to create something like this in our child theme style.css file.
#wp_sidebarlogin-6 {
opacity:0.4;
filter:alpha(opacity=40); /* For IE8 and earlier */
}