<a class="btn btn-primary" href="/periodico-soy-amarillo"  title="< Volver">< Volver</a>
<style>
    
    .btn {
    color: #0f2240;
    text-transform: uppercase;
    font-size: 14px;
    background: #ffd331;
    display: inline-block;
    padding: 10px 12px;
    margin-right: 5px;
    position: relative;
    cursor: pointer;
    }
    
    .btn-primary {
    border-color: #245580;
    }

Soy Amarillo Nº21