OptionList layout to DialogScreen cancel the margin left&right black-line?

[Yurii-huang]

DialogScreen {
    align: center middle;
    background: $primary 0%;
}

DiskOptions> OptionList {
    width: 50%;
    background: #bbbbbb;
    margin-left: 0;
    margin-right: 0;
}

How should the black vertical line pointed by the arrow in the picture be removed?

[Yurii-huang]

should change the focus border

DiskOptions> OptionList:focus {
    border: double $accent;
}