if ( !function_exists( 'html_var_dump' ) ) {
    function html_var_dump( $data ) {
        $out = "\n<pre class='html-var-dump'";
        $out .= " style='border: 1px solid #ccc; padding: 7px;'>\n";

        ob_start( );
        var_dump( $data );
        $out .= esc_html( ob_get_contents( ) );
        ob_end_clean( );

        $out .= "\n</pre>\n";

        return $out;
    }
}

Even though I tend to use print_r more often than var_dump, there are times where the type data that var_dump provides can be very helpful. Unfortunately var_dump will always display data, so it needed to be wrapped in a few output control functions ( ob_start, ob_get_contents, and ob_end_clean ) to capture it.