Just ran into a version problem where my devel environment was running a cakephp version ahead of my live

In cake 2.4.1 this works:

// in layout
   echo $this->fetch('css');

// in view
$this->Html->css(
    array( 
'mio-accordion'
        ),
    array('block' => 'css')
    );

But in 2.3.1 you have to do this:

//same thing in layout as above 

// this in view
// you can put this options array
// strait into the css() block
$options = array(
  'inline' => false,
  'block' => 'css'
);

//notice this has three args
//the script file name as a file or 
// an array 
// 2nd arg is null
// then your options and html attribs.

$this->Html->css(
    'mio-accordion',
    null,  
    $options
);