Tim,
You want to apply the following styling to textarea elements to get rid of the border and background:
#q? textarea {
background: none !important;
border: none !important;
}
You need the "!important" at the end to override the default styling, and you want to replace the "?" with the value you see for the parent, which you can find in the CSS/JavaScript tab.
It looks like your fields are in a table. If that is the case, it makes things a little easier because a table, section, etc. allows you to use the id of the table and apply it to every child textarea in one go.
For example, if the table/section containing those multi-lines is "q4" then you would apply the CSS styling to "#q4 textarea" and it should affect them all.
You might want to adjust text color and such as well since disabled text looks different.