site is not working after elixir installation.

My laravel version is 5.3 and have installed elixir and all the required dependancies. following is my gulpfile.js code

var elixir = require('laravel-elixir');
var publicCssPath = './public/css/';
elixir(function(mix) {
mix
.styles([
publicCssPath + 'bootstrap.css',
publicCssPath + 'style.css',
publicCssPath + 'et-line-fonts.css',
publicCssPath + 'animate.min.css',
publicCssPath + 'bootstrap-dropdownhover.min.css',
publicCssPath + 'style1.css'
], 'public/assets/css/frontend.css');
});

when i run gulp. it gives creates the new file in given directory. but when i open my site on browser it gives ERR_CONTENT_DECODING_FAILED error.

Please help me to solve this issue. i am new in elixir.