because the css properties work only in HTML and not in the external css

<button id="btn-info" type="button"></button>

When I put the selector with the properties in external css it does not work but if you put it directly into the html style it works fine.

#btn-info{
    display: block!important;
    background-image: url(icons/categorias/informatica/headset.svg);
    width: 100px;
    height: 100px;

    border: solid 1px #ccc;
    border-radius: 50%
}

When I go into source browser menu browser, I see that my css snippet has been ignored, but if I paste the same CSS snippet there it works with hesitancy.  

How can I modify properties by my CSS file?