I assume that you set the border via .css("border","1px solid red")
or something alike.
jQuerys css() function sets the style inline; it modifies the style attribute:
<input style="border:1px solid red;" />
Styles defined in a CSS file are overwritten by inline styles.
To reset the style, the best way is to delete the inline-style by passing something useless to the browser, normally an empty string:
$("input").css("border","");
The browser can't render that rule and will fall back to the rules defined in your CSS file.
If you wish to reset the style to the browser's default, use the "initial" keyword.