/* Darker than -fx-background and used to draw boxes around text boxes and
     * password boxes.
     */
    -fx-text-box-border: ladder(
        -fx-background,
        black 10%,
        derive(-fx-background, -15%)
    );

should be

    /* Darker than -fx-background and used to draw boxes around text boxes and
     * password boxes.
     */
    -fx-text-box-border: ladder(
        -fx-background,
        black 10%,
        derive(-fx-background, -15%) 30%
    );