html tutorial - How to expand select box to its default width on focus using CSS - html5 - html code - html form
Answer: Use CSS :focus Pseudo-class
By default the size of the <select> element is depend on the size of the largest <option> text. However, sometimes it is useful to set a fixed width to the select box and increase its size back to the original size when the user try to select some option i.e. on focus.