• Download the zip file and extract the folder.
• Move the document to the .themes folder located in the personal folder

• Includes the theme Linux-Mint for gtk / gtk + with personal modifications.

.panel-left {
background color: rgba (20, 20, 20, 0.8);
}

.panel-right {
background color: rgba (20, 20, 20, 0.8);
}

.panel-top {
background color: rgba (20, 20, 20, 1);
}

.panel-bottom {
background color: rgba (20, 20, 20, 1);
}

Modify the last value, in the case of the left / right is 0.8 and top / bottom part is 1. You can only put a value from 0 to 1 taking into account decimals, with total transparency 0 and no transparency 1.