Based on what I have seen, If we have a table consist of both text and string...text will remain same (based on external css rules) and string will shrink. Unless all of them are changed equally using the external css. But I agree with you Richard, there are no elastic text area. the bootstrap is responsive as a default.
<script>$('textarea').css('width','20%').css('height','70px');</script>
<style>#header2 {
background-color:skyblue;
color:white;
text-align:left;
padding: 0.1%;
width: 15%;
height: 4%;
}</style>
Its better to define the width as a % as it will shrink the page based on % defined in the css rules. Then its responsive all the way and always will even with external css.