How to fix "DOM Exception 18" gulp-uncss error?

Question

gulp.js

gulp.task('build', function() {

  var delDistr = del.sync('dist/');

  var buildHeaderCss = gulp.src('app/css/header.min.css')
    .pipe(uncss({
      html: ['app/index.html']
    }))
    .pipe(gulp.dest('dist/css/'))

});

body {
  font-family: "Open Sans", sans-serif;
  color: #666;
  height: 100vh; }

.cust-flex {
  display: -webkit-box;
  display: -webkit-flex;
  display: -ms-flexbox;
  display: flex;
  -webkit-box-align: center;
  -webkit-align-items: center;
  -ms-flex-align: center;
  align-items: center;
  height: 100%; }

.cust-mh {
  min-height: 15rem; }

.cust-filter {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  z-index: 0; }

.title-block {
  font-family: "Kurale", serif;
  font-size: 2.5rem;
  text-transform: uppercase;
  font-weight: 600;
  margin-bottom: 5rem;
  word-wrap: break-word; }

.firm-color, i {
  color: #4f8cff; }

.btn-cust {
  background-color: #4f8cff;
  border: 0.1rem solid #2d6add;
  color: #fff; }
  .btn-cust:hover {
    background-color: #71aeff;
    color: #fff;
    cursor: pointer; }

section {
  padding: 5rem 0; }

.firm-font {
  font-family: "Kurale", serif; }

header {
  position: relative;
  background: url(/img/bg.jpg) no-repeat 50% 50%;
  background-size: cover; }
  header .filt1 {
    background-color: rgba(0, 0, 0, 0.5); }
  header h1 {
    font-size: 5rem; }

/* Our product */
.our-product p {
  font-size: 1.25rem; }

/*==========  Desktop First Method  ========== */
/* Large Devices, Wide Screens */
@media only screen and (max-width: 1200px) {
  /* */ }

/* Medium Devices, Desktops */
@media only screen and (max-width: 992px) {
  header h1 {
    font-size: 4rem; } }

/* Small Devices, Tablets */
@media only screen and (max-width: 768px) {
  .our-product p, p {
    font-size: 0.9rem; }
  section {
    padding: 3rem 0; }
  .title-block {
    font-size: 2rem; }
  header h1 {
    font-size: 3rem; }
  .our-product {
    /* background: url(/img/skin_panel.png) no-repeat 110% 100%;
    background-size: auto; */
    position: relative;
    overflow: hidden; }
    .our-product .bg-mobile {
      position: absolute;
      right: -8rem;
      top: 15rem;
      width: 15rem;
      height: 15rem;
      background: url(/img/skin_panel.png) no-repeat 50% 50%;
      background-size: cover; }
  /*Disable Animation on Mobile Devices */
  .animated {
    /*CSS transitions */
    -webkit-transition-property: none !important;
    transition-property: none !important;
    /*CSS transforms */
    -ms-transform: none !important;
    -webkit-transform: none !important;
    transform: none !important;
    /*CSS animations */
    -webkit-animation: none !important;
    animation: none !important; } }

/* Extra Small Devices, Phones */
@media only screen and (max-width: 480px) {
  header h1 {
    font-size: 2.5rem; }
  header h3 {
    font-size: 1.3rem; }
  .title-block {
    font-size: 1.5rem; } }

/* Custom, iPhone Retina */
@media only screen and (max-width: 320px) {
  /* */ }

/*==========  Mobile First Method  ========== */
/* Custom, iPhone Retina */
@media only screen and (min-width: 320px) {
  /* */ }

/* Extra Small Devices, Phones */
@media only screen and (min-width: 480px) {
  /* */ }

/* Small Devices, Tablets */
@media only screen and (min-width: 768px) {
  /* */ }

/* Medium Devices, Desktops */
@media only screen and (min-width: 992px) {
  /* */ }

/* Large Devices, Wide Screens */
@media only screen and (min-width: 1200px) {
  /* */ }

c:\projects\kzn_gips_panel>gulp build
[13:55:37] Using gulpfile c:\projects\kzn_gips_panel\gulpfile.js
[13:55:37] Starting 'build'...
[13:55:37] Finished 'build' after 23 ms
SecurityError: DOM Exception 18: An attempt was made to break through the security policy of the user agent.
local:19 in n
local:19 in loadLocalStorageCSS

What's wrong? Previously, everything compiled without problems, they write that there may be errors in css. Perhaps this is the case, because empty css compiles without problems.
It has something to do with the html file