Contenteditable Height transition

Question

I have a contenteditable div which grows as the user types.

I now need to transition the height so that when the user presses Enter, the div would grow s

Answer 1

Final solution based on Orland's answer. Thank you, bootstrap!

HTML

    Testing 
 one two three

CSS:

@keyframes lineInserted {  
    from { height: 0; }
    to { height: 20px; }  /* cons: hardcoded height */
}

div[contenteditable] > div {
    animation-duration: 200ms;
    animation-name: lineInserted;
}

div[contenteditable]{
    height : auto !important;
    overflow: auto;
    line-height : 20px;
}