:root
{
    --color_base_boton:#E0A000;
    --color_base_boton_hover: #616161;
}
/*xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx*/
.boton_St_3
{
    width: 250px;
    height: 50px;
    border-radius: 5px;
    background-color: var(--color_base_boton);
    border: 2px solid white;
    color: white;
    text-decoration: none;
    font-size: 1.2rem;
    font-weight: 700;
    display: flex;
    align-items: center;
    justify-content: center;
    overflow: hidden;
    transition: all 0.3s ease;
}
.cont_fondo_movil
{
    width: 0%;
    height: 0%;
    background-color: var(--color_base_boton_hover);
    display: flex;
    align-items: center;
    justify-content: center;
    transform: width;
    transition: all 0.3s ease;
}

.boton_St_3:hover .cont_fondo_movil
{
    width: 100%;
    height: 100%;
}