To get this, you need to put the code below into your CSS box which is found when you customize your blog.

iframe#tumblr_controls {right:3px !important; position: fixed !important;-webkit-transition: opacity 0.7s linear;opacity: 0.2;-webkit-transition: all 0.8s ease-out;-moz-transition: all 0.8s ease-out;transition: all 0.8s ease-out;}

iframe#tumblr_controls:hover{-webkit-transition: opacity 0.7s linear;opacity: 1;-webkit-transition: all 0.4s ease-out;-moz-transition: all 0.4s ease-out;transition: all 0.4s ease-out;}