How can I change the font to black please

My form has a light color font and I will like to change it to black.

You can change the font color by clicking on the Designer icon -> Font Color: 

You can also inject this CSS code: 

.form-all{

    color: #FFFFFF;

}

This guide will help you to inject the code to your form: How-to-Inject-Custom-CSS-Codes

Hope this helps.