I don't know how to wrap it up.

{
  "name": "test",
  "manifest_version"—2,
  "version": "1.0",
  "permissions": ["tabs", "storage" ],
  "browser_action": {
    "default_title": "Mister test",
    "default_popup": "popup.html"
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    ppersistent :—false
  },
  "content_scripts":[
    {
      "js": ["content_script.js",
      "matches": ["http://*/*", "https://*/*",
      "run_at": " document_end"
    }
  ]
}

 "When you launch a pop-up, find out if you saved the memo in that url and pass it to content_script.js"
chrome.tabs.query({active:true, lastFocusedWindow:true},tabs=>{
  chrome.storage.local.get([tabs[0].url], item=>{
    // When you launch a pop-up, look for the url to save the note.
    // If available: Show modal at text location stored in chrome.storage
    if(item[tabs[0].url]){
       chrome.tabs.sendMessage(tabs[0].id, {content:item[tabs[0].url].content,posX:item[tabs[0].url].posX,posY:item[tabs[0].url].posY});
    }
    // If not: Show modal in blank text box in default position
    else{
       chrome.tabs.sendMessage(tabs[0].id, {content:', posX:0, posY:0});
    }
  });
});

chrome.runtime.onMessage.addListener(content, sender, sendResponse)=>{
  chrome.tabs.query({'active':true,'lastFocusedWindow':true},tabs=>{
    const url=tabs[0].url;//{'active':true, 'lastFocusedWindow':true} tabs (there is only one)
    let data = {};
    // link location and content to a URL
    data[url] = {
      content:content,
      posX: 100,
      posY: 100
    };
    // preservation
     chrome.storage.local.set(data);
  });
  // Reply "I saved it"
   sendResponse('saved');
});

const save=(content)=>{//save(textbox.value)
  chrome.runtime.sendMessage(content,res=>{
      console.log(res);
  });
};
chrome.runtime.onMessage.addListener(message, sender, sendResponse)=>{
  const modalfrm= document.getElementById('ex-memo');
  if(modalfrm!=null)return;
  const modal= document.createElement('div');
  modal.id = 'ex-memo';
  // modal.style.width='500px';
  // modal.style.height='100px';
  modal.style.zIndex='2147483647';
  modal.style.position='fixed';
  modal.style.left=`${message.posX}px`;
  modal.style.top=`${message.posY}px`;
  console.log("modal.style.left:" +modal.style.left);
  console.log("modal.style.top:"+modal.style.top);
  console.log("modal.style.width:" + modal.style.width);
  console.log("modal.style.height:"+modal.style.height);
  const textbox= document.createElement('textarea');
  textbox.style.width='600px';
  textbox.style.height='200px';
  textbox.style.backgroundColor='rgb(67,67,67)';
  textbox.style.color='rgb(51,166,184)';
  textbox.value=message.content;
  modal.appendChild(textbox);
  const saveButton= document.createElement('button');
  saveButton.onclick=()=>save(textbox.value);
  saveButton.innerText='Save';
  modal.appendChild(saveButton);
  document.body.appendChild(modal);
  console.log("function");
  modal.addEventListener ('musedown', mdown);
  modal.addEventListener('touchstart',mdown);
  // "Function when mouse is pressed"
  function mdown(e){
      console.log("mdown");
      This.classList.add("drag");
      // Absorbs differences between touched and mouse events
      if(e.type==="mousedown"){
          var event=e;
      } else{
          var event=e.changedTouches[0];
      }
      // Get relative coordinates in elements
      posX=event.pageX-this.offsetLeft;
      posY = event.pageY-this.offsetTop;
      // Callback to Move Event
      document.body.addEventListener("mousemove", mmove);
      document.body.addEventListener("touchmove", mmove);
  }
  // "Fire when mouse cursor moves"
  function mmove(e){
      console.log("mmove");
      // Get the element you are dragging
    　vardrag= document.getElementsByClassName("drag")[0];
      //Similarly absorbs the difference between mouse and touch
      if(e.type==="mousemove"){
          var event=e;
      } else{
          var event=e.changedTouches[0];
      }
      // Suppresses default behavior so that the screen does not move when flicking
      e.preventDefault();
      // Move the element where the mouse moved
      drag.style.top =event.pageY-posY+"px";
      drag.style.left=event.pageX-posX+"px";
      // Fire when mouse button is released or cursor is released
      drag.addEventListener("mouseup",mup);
      document.body.addEventListener("mouseleave",mup);
      drag.addEventListener("touchend",mup);
      document.body.addEventListener("touchleave",mup);

        // "Fire when the mouse button is up"
  function mup(e){
    console.log("mup");
    vardrag= document.getElementsByClassName("drag")[0];
    // Clearing the Move Event Handler
    document.body.removeEventListener("mousemove", mmove);
    drag.removeEventListener("mouseup",mup);
    document.body.removeEventListener("touchmove", mmove);
    drag.removeEventListener("touchend",mup);
    // Also erase class name .drag
    drag.classList.remove("drag");
  }

  }
});