问如何使HTML表单按钮在屏幕上放置一个用户可以输入文本的下拉式表单列表

EN

let daysPlan = "";

function updateMyday() {
  var selectBox = document.getElementById("odays");
  var div = document.getElementById("daysUp");
  //var selectOption = selectBox.options[selectBox.selectedIndex];
  var selectedValue = selectBox.options[selectBox.selectedIndex].value;

  event = window.prompt("what's up that day ?");

  // to show on the page somewhere 
  var newDay = document.createElement("div");
  newDay.textContent = selectedValue + " : " + event;
  div.appendChild(newDay);
  // end show 

  // store it , a variable, a localstorge, else ?
  daysPlan += selectedValue + " : " + event + "\n"
  console.log(daysPlan) // to use and send once submitting 
}

#odays {
  display: none;/* not sure i understood that part*/
}

form {
  float: left;
}

#daysUp {
  white-space: pre;
}

<form><label for='odays'> Open Days: </label><br>

  <input type='button' onclick='let e =document.getElementById("odays"); e.style.display="block";' value='Add Day'><br>

  <select id='odays' name='odays' onchange="updateMyday()">
    <option>Choose a day </option>
    <option value='monday   '> Monday </option>
    <option value='tuesday  '> Tuesday </option>
    <option value='wednesday'> Wednesday </option>
    <option value='thursday '> Thursday </option>
    <option value='friday   '> Friday </option>
    <option value='saturday '> Saturday </option>
    <option value='sunday   '> Sunday </option>
  </select>
</form>
<div id="daysUp">
</div>