スクロール可能な Div をサイズ変更可能な外側の Div の一番下に固定したままにする方法は?

.outer-div {
  display: flex;
  flex-direction: column-reverse;
}

.scrollable-div {
  flex: 1;
  overflow: auto;
}

/* Reset webkit, including edge */
.scrollable-div-text {
  overflow: visible;
}

@supports (-ms-accelerator: true) {
  .scrollable-div-text {
    overflow: auto;
  }
}

// Check if at bottom of scrollable div
function scrollAtBottom(el) {
  return (el.scrollTop + 5 >= (el.scrollHeight - el.offsetHeight));
}

// Update scroll position if at the bottom
function updateScroll(el) {
  el.scrollTop = el.scrollHeight;
}

// Function to resize input and adjust scroll position if needed
function resizeInput() {
  const scrollableDiv = document.getElementById('scrollable-div');
  const input = document.getElementById('input');
  
  // Toggle input height
  input.style.height = input.style.height === '40px' ? '120px' : '40px';

  // Check if scrolled to the bottom and update scroll position if needed
  if (scrollAtBottom(scrollableDiv)) {
    updateScroll(scrollableDiv);
  }
}