I made it by css in codemirror 6.

My html structure

<div class="code-editor-container">
    <div class="cm-editor">...</div>
</div>

SCSS

.code-editor-container {
  background-color: white;
  border: 1px solid lightgray;
  position: relative;

  resize: vertical;
  overflow: auto;
  max-height: 600px;
  min-height: 2rem;

  .cm-editor {
    height: 100%;
    max-height: 600px;
  }
}

Picture