Javascript libraries not loading from block class I am working on porting module to drupal 8. 

My block code is as follow

public function build() {
  $delta= $this->getDerivativeId();
  $num           = str_replace('dexp_layerslider_block_', '', $delta);
  $sid = $this->configuration['dexp_layerslider_block_slide_'.$num];
  $block_id = $this->getDerivativeId();
  $slideshow = dexp_layerslider_load($sid);
  if (!$slideshow){
     return 'No slider selected';
  } 
  $content =   array(
      'id' => $sid,
      'slides' => $slideshow->slides,
      'settings' => $slideshow->settings
     );
   return array(
     '#theme' => 'dexp_layerslider_slides',
     '#items' => $content,
     '#attached' => array(
        'library' => array('dexp_layerslider/dexp.block'),
        ),
      );
}
 
my yaml file: 

dexp.slides:
  version: 1.x
  css:
    theme:
      plugins/font-awesome/css/font-awesome.min.css: {}
      css/admin.style.css: {}
      plugins/rs-plugin/css/settings.css: {}
  js:
    js/dexp.layerslider.js: {}
    js/layeroption.js: {}
    js/admin.layerslider.js: {}
    plugins/rs-plugin/js/jquery.themepunch.revolution.min.js:  {}
    plugins/rs-plugin/js/jquery.themepunch.tools.min.js:  {}
 dexp.block:
  version: 1.x
  css:
    theme:
      plugins/rs-plugin/css/settings.css: {}
      css/layerslider.css: {}
  js:
    plugins/rs-plugin/js/jquery.themepunch.revolution.min.js:  {}
    plugins/rs-plugin/js/jquery.themepunch.tools.min.js:  {}
  dependencies:
    - core/drupal
    - core/jquery

my theme function :

  $themes['dexp_layerslider_slides'] = array(
    'template' => 'slides',
    'path' => $path . '/theme',
    'pattern' => 'layerslider__',
    'preprocess functions' => array(
      'template_preprocess',
      'dexp_layerslider_preprocess_slides'
    ),
    'variables' => array('items'=>null),
  );

None of  javascript and css files are load , when i try to access items in twig template {{ items }} nothing gets printed , though if write random string in the my slide.html.twig file it get printed. where i could be going wrong?
You don't have a "dexp.slide" defined in your libraries.yml file. Only "dexp.block".

You're trying to attach a library that doesn't exist.