bootstrap 4卡文本关闭卡文本

I'm trying to put a text in a card-text paragraph but when I put It that happens:

the text goes out of the container

I'm trying to fix it but I can't, I'm without any kind of idea of how to fix it. The source code:

<div class='card'>
      <img class='card-img-top img-fluid' width="100%" src="{$post['imagen']}" alt=''>
      <div class='card-block'>
        <h4 class='card-title'>{$post['titulo']}</h4>
        <p class='card-text'>{$post['descripcion']}</p>
        <p class='card-text'><h6><a href="./categoria/{$post['categoria']}"><span class="tag tag-success"><i class="fa fa-tag" aria-hidden="true"></i> {$post['categoria']}</span></a></h6></p>
        <p class="text-muted card-text hidden-sm-up"></i>{$fecha}</p>
        <a href="./post/{$post['id']}" class='btn btn-primary hidden-sm-down'><i class="fa fa-eye" aria-hidden="true"></i> Leer más</a>
        <a href="./post/{$post['id']}" class='btn btn-primary hidden-sm-up btn-block'><i class="fa fa-eye" aria-hidden="true"></i> Leer más</a>
        <p class="pull-xs-right text-muted card-text hidden-sm-down">{$fecha}</p>
      </div>
    </div>

I'm also using PHP. Thanks for the help :)

As

@NuclearPeon

says, the word-wrap in the styles.css