Add custom CSS code to the form itself that will override your other code.
open the form. go to form settings > form theme > select the gear icon
The code below work well. I also included an image of the form with color for reference.
.mktoForm input[type=text],
.mktoForm input[type=url],
.mktoForm input[type=email],
.mktoForm input[type=tel],
.mktoForm input[type=number],
.mktoForm input[type=date],
.mktoForm select.mktoField,
.mktoForm textarea.mktoField{
-webkit-appearance: none;
color:#00a0df;
}