style(styles) {
        if (styles.separatorBorder.isTransparent()) {
            this.el.classList.remove('separator-border');
            this.el.style.removeProperty('--separator-border');
        }
        else {
            this.el.classList.add('separator-border');
            this.el.style.setProperty('--separator-border', styles.separatorBorder.toString());
        }
    }
Fires whenever the user double clicks a {@link Sash sash}.