The safe, proper way to do this is both shorter and more readable!

Both with jQuery:

    const $newdiv = $('<div>')
      .addClass(messageDivClass)
      .text(inputTextBox.value)
      .css({'opacity': '0.95'});

and without:

    const newdiv = document.createElement('div');
    newdiv.classList.add(messageDivClass);
    newdiv.innerText = inputTextBox.value;
    newdiv.style.opacity = '0.95';