Ah, I see you meant the colour of the placeholder text in the form fields.
You can fix it like this:
1. Since you are using the Elementor widget, first add a class to the form (this is so that you can target that specific form instead of all the review forms on your website (in case some of them are not used on a dark background)):
2. Add the following custom CSS to your website:
form.dark-form ::placeholder {
color: rgba(0,0,0,.8);
}
Alternatively, you could also do this instead:
.glsr form.dark-form {
color: #fff;
}
.glsr form.dark-form ::placeholder {
color: rgba(255,255,255,0.9);
}
.glsr form.dark-form input.glsr-input,
.glsr form.dark-form textarea.glsr-textarea {
background-color: rgba(255,255,255,0.2);
border-color: rgba(255,255,255,0.2);
}
.glsr form.dark-form input.glsr-input:focus,
.glsr form.dark-form textarea.glsr-textarea:focus {
background-color: rgba(255,255,255,0.2);
border-color: #39c1bd;
box-shadow: 0 0 0 1px #39c1bd;
}
.glsr form.dark-form input.glsr-input.glsr-is-invalid:focus,
.glsr form.dark-form textarea.glsr-textarea.glsr-is-invalid:focus {
border-color: #e02424;
box-shadow: 0 0 0 1px #e02424;
}