If you press the save button, it will get stuck.

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");
  }
});