background.js

// Copyright 2018 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

'use strict';

  chrome.runtime.onInstalled.addListener(function() {
    chrome.storage.sync.set({color: '#3aa757'}, function() {
      console.log('The color is green.');
    });
    chrome.declarativeContent.onPageChanged.removeRules(undefined, function() {
      chrome.declarativeContent.onPageChanged.addRules([{
        conditions: [new chrome.declarativeContent.PageStateMatcher({
          pageUrl: {schemes: ['http','https']},
        })],
            actions: [new chrome.declarativeContent.ShowPageAction()]
      }]);
    });

  });

  chrome.commands.onCommand.addListener(function(command) {
    if (command === "toggle-gradient") {
      chrome.tabs.query({active: true, currentWindow: true}, function(tabs) {
        chrome.tabs.sendMessage(tabs[0].id, {toggle: true});
      });
    };
  });