// ---------------------------------------------------------
// str-capitalize
// Make string's first character uppercase
//
// Required arguments:
// `$string` String
//
// Example of use:
// str-capitalize('differs')
//
// @return String
// ---------------------------------------------------------
@function str-capitalize ($string) {
  @if type-of($string) != 'string' {
    @error 'The argument $string: `#{$string}` is of incorrect type: `#{type-of($string)}`. Type of `String` is required!';
  }

  @return to-upper-case(str-slice($string, 1, 1)) + str-slice($string, 2);
}