barcode_scanner_admin/assets/fonts/material-design/scss/_icons.scss

@each $key, $value in $mdi-icons {
    .#{$mdi-css-prefix}-#{$key}:before {
        content: char($value);
    }
}
.#{$mdi-css-prefix}-blank:before {
    content: "\F68C";
    visibility: hidden;
}