chromium/third_party/blink/renderer/core/html/forms/resources/list_picker.css

select {
    display: block;
    overflow-y: auto;
    border-radius: 0px;
    outline: none;
}

select hr {
    border-style: none;
    border-bottom: 1px solid black;
    margin: 0 0.5em;
}

option, optgroup {
    padding-inline-end: 2px;
}

.wrap option {
    white-space: pre-wrap;
}