::-webkit-scrollbar-button with content

I've tried to design the webkit scrollbar like Visual Studio.

Example:

My question is, how i can set the ::-webkit-scrollbar-button like the example?

Here is my Code:

::-webkit-scrollbar-button {
    height: 10px;
    content: "▲";
    color: rgb(255, 255, 255);
    background: rgb(255, 0, 0);
}

Output:

It is possible to use content: ""; property to set an UTF-Character like ▲ or ▼ ? Why it would'nt display?

Here is a Fiddle