I solved it by adding the url for the background image at the end of the line.
.page{
background: -moz-linear-gradient(rgba(0,255,0,.5)), url('https://www.nepalitrek.com/wp-content/uploads/2017/09/langtang-gosaikundaintro.jpg') no-repeat;
background: -webkit-gradient(rgba(0,255,0,.5)), url('https://www.nepalitrek.com/wp-content/uploads/2017/09/langtang-gosaikundaintro.jpg') no-repeat;
background: -webkit-linear-gradient(rgba(0,255,0,.5)), url('https://www.nepalitrek.com/wp-content/uploads/2017/09/langtang-gosaikundaintro.jpg') no-repeat;
background: -o-linear-gradient(rgba(0,255,0,.5)), url('https://www.nepalitrek.com/wp-content/uploads/2017/09/langtang-gosaikundaintro.jpg') no-repeat;
background: -ms-linear-gradient(rgba(0,255,0,.5)), url('https://www.nepalitrek.com/wp-content/uploads/2017/09/langtang-gosaikundaintro.jpg') no-repeat;
background: linear-gradient(rgba(0,255,0,.5)), url('https://www.nepalitrek.com/wp-content/uploads/2017/09/langtang-gosaikundaintro.jpg') no-repeat;
margin: 0 auto;
padding: 0;
}