CSS Incompatibility with jquery blockUI in IE 8

I'm using jquery 1.11.0 in> along with the plugin jquery-blockui < in> 2.66.0 and when blocking the screen, div gets white background in IE8 and earlier.

Here are the images:

The call to blockUI:

$.blockUI({
    message: "<p style=\"font-weight: bolder; color: white;\">N&atilde;o houve resultado para o seu filtro.<br /><br /><a class=\"fecharBlockUI\">Fechar</a></p>",
    timeout: 5000,
    onOverlayClick: $.unblockUI
});

I know I should do a CSS hack, but I am not familiar with front end, could anyone explain to me how to keep the behavior equal to the first image also in IE 8 and earlier?

As requested, follows the css style change:

$.blockUI.defaults.css = {
    border: "none",
    backgroundColor: "rgba(255, 255, 255, 0)",
    textAlign: "center",
    padding: 0,
    margin: 0,
    width: "30%",
    top: "40%",
    left: "35%",
    color: "#000000",
    cursor: "wait" 
};