Open the inspector and add the following as a new CSS rule (once you’ve added any rule, you can subsequently edit the inspector stylesheet found under “Sources” on Chrome)

inspector-stylesheet.css

.blob-code span:before {
    background: #fdfd9c;
    color: #a2a2a2;
    content: attr(class);
    font-family: sans-serif;
    font-size: 0.7em;
    padding: 0 0.2em;
    vertical-align: middle;
}