Please try to use the following CSS code. Second part of the code below should make mobile menu button green, for clear visibility.
You can add CSS code to your site with Simple Custom CSS plugin (just copy CSS code and paste it in Dashboard → Appearance → Custom CSS after installing and activating the plugin). Also you can add CSS code directly to
style.css file of your child theme.
color: rgb(109, 128, 88);
Please feel free to ask any other questions that you might have.
Kind Regards, Roman.