In modena.css, the text fill for highlighted, focused text is hard-coded as "white". This makes selected text unreadable if a -fx-accent is changed to a light color. As an example:
.root {
-fx-base: #3f474f;
-fx-accent: #e7eff7 ;
-fx-default-button: #7f878f ;
-fx-focus-color: #efefef;
        -fx-faint-focus-color: #efefef22;
}

The text fill rule should probably be based on a ladder, using -fx-highlight-fill as the basis for the ladder. Something like:

.text-input:focused {
    /* ... */
    -fx-highlight-text-fill: ladder(
        -fx-highlight-fill,
        -fx-light-text-color 45%,
        -fx-dark-text-color 46%,
        -fx-dark-text-color 59%,
        -fx-mid-text-color 60%
    );
    /* ... */
}