Instead of box-sizing: border-box for inputs, textarea and others

embed-inputs.jquery.js

function embedInputs($selector) {
	$selector.each(function() {
		var $this = $(this);

		$this.width(1);
		if($this.is('textarea')) {
			$this.css({'min-width': '', 'max-width': ''});
		}

		var additionalWidth =
				parseInt($this.css('border-left-width')) +
				parseInt($this.css('border-right-width')) +
				parseInt($this.css('margin-left')) +
				parseInt($this.css('margin-right')) +
				parseInt($this.css('padding-left')) +
				parseInt($this.css('padding-right')),
			parentWidth = $this.parent().width(),
			countedWidth = parentWidth-additionalWidth;

		setTimeout(function() {
			$this.width(countedWidth);
			if($this.is('textarea')) {
				$this.css({
					'min-width': countedWidth,
					'max-width': countedWidth
				});
			}
		}, 10); // avoiding lags while window resizing (for big JS files)
	});
}

init.js

$(document).ready(embedInputs($('.embed')));
$(window).resize(embedInputs($('.embed')));