Option height will be ignored if there is also min-height that has bigger value, because this is was it was designed for.

Docs: https://www.w3schools.com/cssref/pr_dim_min-height.asp

Based on demo that you provided in comments, you have this block in CSS:

textarea {
  font-size: 12px;
  line-height: 21px;
  color: #444;
  border: 1px solid #e1e1e1;
  width: 100%;
  max-width: 100%;
  height: 168px;
  min-height: 168px; // HERE
  padding: 6px 9px;
}

Like you see, there is min-height: 168px;.

All you have to do is to remove this, or overwrite it if for some reason you cannot do this.

textarea, .dlk_q {
  width: 98%;
  height: 50px !important;
  min-height: 0 !important; // ADD THIS
}

Since there was a min-heigth setting I’ve reset it like this:

textarea {
    min-height:initial; /* resets the value set by theme */
}

I have the following HTML code:

<textarea type="text" class="dlk_q" rows="2" cols="98%" name="q[]">

in a page that has other stylesheets but I added this CSS right before the textarea in my HTML:

textarea, .dlk_q {
    width: 98%;
    height: 50px !important;
}

however the height of the textarea appears to be much bigger than 50 (ie the height is ignored)
What can I do about this?