Looks like the enhanced editor uses an iframe. Changing the css to the following allows to resize the table cell it is inside, which has the nice side effect that the text area automatically shares the same size when you toggle the editor mode.
Code:
/* Element | https://www.esoui.com/forums/newreply.php?do=newreply&noquote=1&p=41148 */
#vB_Editor_001_iframe {
/* width: 740px; */
/* height: 250px; */
width: 100%;
height: 100%;
}
/* Element | https://www.esoui.com/forums/newreply.php?do=newreply&noquote=1&p=41148 */
td.controlbar:nth-child(1) {
display: block;
resize: both;
overflow: auto;
padding: 4px;
}
/* Element | https://www.esoui.com/forums/newreply.php?do=newreply&noquote=1&p=41148 */
#vB_Editor_001_textarea {
resize: none;
}