PostCSSでCSSを変換 ref: http://qiita.com/t-okushima/items/e910ef9dd858ac6634e8

file0.txt

npm install --save-dev gulp-postcss autoprefixer

file1.js

'use strict';

var gulp = require('gulp'),
    postcss = require('gulp-postcss');

// apply PostCSS plugins
gulp.task('css', function() {
  return gulp.src('css/test.css')
    .pipe(postcss([
      require('autoprefixer')({})
    ]))
    .pipe(gulp.dest('dest/css/test.css'));
});

file2.css

.bg-bubbles {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  z-index: 1;
}
.bg-bubbles li {
  position: absolute;
  list-style: none;
  display: block;
  width: 40px;
  height: 40px;
  background-color: rgba(255, 255, 255, 0.15);
  bottom: -160px;
  border-radius:50%;
  animation: square 25s infinite;
  transition-timing-function: linear;
}

file3.css

.bg-bubbles {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  z-index: 1;
}
.bg-bubbles li {
  position: absolute;
  list-style: none;
  display: block;
  width: 40px;
  height: 40px;
  background-color: rgba(255, 255, 255, 0.15);
  bottom: -160px;
  border-radius:50%;
  -webkit-animation: square 25s infinite;
          animation: square 25s infinite;
  -webkit-transition-timing-function: linear;
          transition-timing-function: linear;
}