Color change for placeholder in input not working

By default, gray font is displayed, which does not blend well with a dark background. If in css it is easy to change the background for the input, then I had to find a solution for the text color in the placeholder.

This example helped me solve the problem (the input had the class form-control):

.form-control::-webkit-input-placeholder { /* WebKit, Blink, Edge */
    color:    #ffffff;
}
.form-control:-moz-placeholder { /* Mozilla Firefox 4 to 18 */
    color:    #ffffff;
    opacity:  1;
}
.form-control::-moz-placeholder { /* Mozilla Firefox 19+ */
    color:    #ffffff;
    opacity:  1;
}
.form-control:-ms-input-placeholder { /* Internet Explorer 10-11 */
    color:    #ffffff;
}
::-webkit-input-placeholder {
  color: #fff;
}
::-moz-placeholder { /* Firefox 19+ */
  color: #fff;
}
:-ms-input-placeholder {
  color: #fff;
}
:-moz-placeholder { /* Firefox 18- */
  color: #fff;
}