/* IE9 */
.curtain {
    display: none\0/;
}

/* IE10 */
@media screen and (-ms-high-contrast: active), (-ms-high-contrast: none) {
    .curtain {
        display: none;
    }
}

@media all and (-ms-high-contrast:none){
  *::-ms-backdrop, .curtain { display: block; } /* IE11 */
}