Problem with HTTPS and font-faces

After activating a Let's Encrypt certificate to use HTTPS on my website, I can not load the @ font-faces and the icons are seen correctly. I'm using Firefox and Chrome in their latest versions for testing.

Originally (when everything worked with HTTP) I had the following in my CSS file:

@font-face {
        font-family: 'cl-xxx';
        src: url('../fonts/cl.eot');
        src: url('../fonts/cl.eot')  format('embedded-opentype'),
             url('../fonts/cl.woff') format('woff'),
             url('../fonts/cl.ttf')  format('truetype'),
             url('../fonts/cl.svg')  format('svg');
}

I have CSS in the "public / css /" folder and the sources in "public / fonts /" and by putting the following URL in the browser, I get the source file: link

If I can load the icon fonts, but placing @ font-face {...} in the header of the HTML document, not in the style sheets as I was doing, and it only works if I use relative or absolute routes with "http", with "https", no.

What have I tried?

1. Al minificar el CSS se eliminan las comillas dentro de url, p.e. url('../fonts/cl.eot'); queda url(../fonts/cl.eot);
Las restaure manualmente.

2. Copiar el directorio de fuentes en el directorio CSS modificando la ruta relativa:

    @font-face {
        font-family: 'cl-xxx';
        src: url('fonts/cl.eot');
        src: url('fonts/cl.eot') format('embedded-opentype'),
        url('fonts/cl.woff')     format('woff'),
        url('fonts/cl.ttf')      format('truetype'),
        url('fonts/cl.svg')      format('svg');
    }


3. Usar rutas adsolutas para las fuentes, tanto con "http" como con "https", p.e.
    @font-face {
        font-family: 'cl-xxx';
        src: url('http://www.cambialibros.es/public/fonts/cl.eot');
        src: url('http://www.cambialibros.es/public/fonts/cl.eot')  format('embedded-opentype'),
             url('http://www.cambialibros.es/public/fonts/cl.woff') format('woff'),
             url('http://www.cambialibros.es/public/fonts/cl.ttf')  format('truetype'),
             url('http://www.cambialibros.es/public/fonts/cl.svg')  format('svg');
    }