You are doing it in the wrong way. An inline style attribute can only contain property declarations, you cannot declare pseudo elements inline.
So try to write your css in a style sheet and link it to your page.
These are the pseudo elements for a textarea
::-webkit-scrollbar
::-webkit-scrollbar-button
::-webkit-scrollbar-track
::-webkit-scrollbar-track-piece
::-webkit-scrollbar-thumb
::-webkit-scrollbar-corner
::-webkit-resizer
A simple example could be:
::-webkit-scrollbar {
width: 12px;
}
::-webkit-scrollbar-track {
-webkit-box-shadow: inset 0 0 6px rgba(0,0,0,0.3);
border-radius: 10px;
}
::-webkit-scrollbar-thumb {
border-radius: 10px;
-webkit-box-shadow: inset 0 0 6px rgba(0,0,0,0.5);
}
::-webkit-scrollbar {
width: 12px;
}
::-webkit-scrollbar-track {
-webkit-box-shadow: inset 0 0 6px rgba(0,0,0,0.3);
border-radius: 10px;
}
::-webkit-scrollbar-thumb {
border-radius: 10px;
-webkit-box-shadow: inset 0 0 6px rgba(0,0,0,0.5);
}
<textarea id="message" rows="4" cols="50"> </textarea>