I just created a custom module for drupal-8 that ad a customizable block. Very simple, is currently working but now i want to add some look to the content of the block.

So my last attempt to achieve this was adding a libraries.yml to the module linking the block_header.css file and at the render array i added #prefix and #suffix with the css tags (div class=’foo’).

The code doesn’t give me any error but it’s not applying the font-weight of the css file.

Could you point me to the right direction?

This are the files:

block_header.libraries.yml

block_header: version: 1.x css:     theme:         css/block_header.css: {} 

BlockHeader.php

<?php  namespace Drupal\block_header\Plugin\Block;  use Drupal\Core\Block\BlockBase; use Drupal\Core\Block\BlockPluginInterface; use Drupal\Core\Form\FormStateInterface;  /**  * Provides a 'Header' Block.  *  * @Block(  *   id = "block_header",  *   admin_label = @Translation("Block Header"),  *   category = @Translation("Block Header"),  * )  */ class BlockHeader extends BlockBase implements BlockPluginInterface {      function block_header_preprocess_html(&$  variables) {         $  variables['page']['#attached']['library'][] = 'Fussion_Modules/block_header/block_header';     }     /**    * {@inheritdoc}    */   public function build() {     $  config = $  this->getConfiguration();      if (!empty($  config['block_header_title']) && ($  config['block_header_text'])) {       $  title = $  config['block_header_title'];       $  descp = $  config['block_header_text'];     }     else {       $  title = $  this->t('<div>Atención! Titulo no configurado!</div> </p>');       $  descp = $  this->t('<div>Atención! Descripción no configurada!</div>');     }     $  block = array         (             'title' => array             (              '#prefix' => '<div class="title"><p>',              '#suffix' => '</p></div>',              '#markup' => t('@title', array('@title' => $  title,)),             ),             'description' => array             (              '#prefix' => '<div class="descp"><p>',              '#suffix' => '</p></div>',              '#markup' => t('@descp', array('@descp' => $  descp,))             ),         );     return $  block;      }   /**    * {@inheritdoc}    */   public function blockForm($  form, FormStateInterface $  form_state) {     $  form = parent::blockForm($  form, $  form_state);      $  config = $  this->getConfiguration();      $  form['block_header_title'] = array(       '#type' => 'textfield',       '#title' => $  this->t('Titulo del Bloque'),       '#description' => $  this->t('Titulo del Bloque'),       '#default_value' => isset($  config['block_header_title']) ? $  config['block_header_title'] : '',     );      $  form['block_header_text'] = array(       '#type' => 'textarea',       '#title' => $  this->t('Descripción'),       '#description' => $  this->t('Descripción del bloque'),       '#default_value' => isset($  config['block_header_text']) ? $  config['block_header_text'] : '',     );      return $  form;   }    /**    * {@inheritdoc}    */   public function blockSubmit($  form, FormStateInterface $  form_state) {     parent::blockSubmit($  form, $  form_state);     $  values = $  form_state->getValues();     $  this->configuration['block_header_title'] = $  values['block_header_title'];     $  this->configuration['block_header_text'] = $  values['block_header_text'];     $  this->configuration['block_header_title'] = $  form_state->getValue('block_header_title');     $  this->configuration['block_header_text'] = $  form_state->getValue('block_header_text');   } } 

block_header.css

.title{     font-weight: 500;     color:darkblue; } 

This is my module structure

Any ideas what i’m doing wrong?