Those 10px the [Caption] tag adds to the attachment div, likely breaking your style in the process, are fixed with the following. The style tag setting width has been commented out.

add_filter( 'img_caption_shortcode', 'cleaner_caption', 10, 3 );

function cleaner_caption( $output, $attr, $content ) {

	/* We're not worried abut captions in feeds, so just return the output here. */
	if ( is_feed() )
		return $output;

	/* Set up the default arguments. */
	$defaults = array(
		'id' => '',
		'align' => 'alignnone',
		'width' => '',
		'caption' => ''
	);

	/* Merge the defaults with user input. */
	$attr = shortcode_atts( $defaults, $attr );

	/* If the width is less than 1 or there is no caption, return the content wrapped between the < tags. */
	if ( 1 > $attr['width'] || empty( $attr['caption'] ) )
		return $content;

	/* Set up the attributes for the caption <div>. */
	$attributes = ( !empty( $attr['id'] ) ? ' id="' . esc_attr( $attr['id'] ) . '"' : '' );
	$attributes .= ' class="wp-caption ' . esc_attr( $attr['align'] ) . '"';
/*	$attributes .= ' style="width: ' . esc_attr( $attr['width'] ) . 'px"';   */

	/* Open the caption <div>. */
	$output = '<div' . $attributes .'>';

	/* Allow shortcodes for the content the caption was created for. */
	$output .= do_shortcode( $content );

	/* Append the caption text. */
	$output .= '
' . $attr['caption'] . '
';

	/* Close the caption </div>. */
	$output .= '</div>';

	/* Return the formatted, clean caption. */
	return $output;
}