I am really not sure on chrome.css. You might try Webkit Scrollbars...
The following is what I use in Vivaldi:
::-webkit-scrollbar {
width: 16px;
}
::-webkit-scrollbar-button:horizontal:decrement {
border-radius: 10px 0px 0px 10px;
background-image: linear-gradient(to bottom, #353535, #555555, #212121, #17171A, #353535);
}
::-webkit-scrollbar-button:horizontal:decrement:hover {
border-radius: 10px 0px 0px 10px;
background-image: linear-gradient(to bottom, #00bdfc, #00759c, #004157, #004157, #00bdfc);
background-color: #00bdfc;
}
::-webkit-scrollbar-button:horizontal:increment {
border-radius: 0px 10px 10px 0px;
background-image: linear-gradient(to bottom, #353535, #555555, #212121, #17171A, #353535);
}
::-webkit-scrollbar-button:horizontal:increment:hover {
border-radius: 0px 10px 10px 0px;
background-image: linear-gradient(to bottom, #00bdfc, #00759c, #004157, #004157, #00bdfc);
background-color: #00bdfc;
}
::-webkit-scrollbar-button:vertical:decrement {
border-radius: 10px 10px 0px 0px;
background-image: linear-gradient(to right, #353535, #555555, #212121, #17171A, #353535);
}
::-webkit-scrollbar-button:vertical:decrement:hover {
border-radius: 10px 10px 0px 0px;
background-image: linear-gradient(to right, #00bdfc, #00759c, #004157, #004157, #00bdfc);
background-color: #00bdfc;
}
::-webkit-scrollbar-button:vertical:increment {
border-radius: 0px 0px 10px 10px;
background-image: linear-gradient(to right, #353535, #555555, #212121, #17171A, #353535);
}
::-webkit-scrollbar-button:vertical:increment:hover {
border-radius: 0px 0px 10px 10px;
background-image: linear-gradient(to right, #00bdfc, #00759c, #004157, #004157, #00bdfc);
background-color: #00bdfc;
}
Modify as needed and hope it does something...