chromium/src/third_party/blink/web_tests/html/dialog/resources/dialog.css

.pseudodialog {
    position: absolute;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
    width: -webkit-fit-content;
    height: -webkit-fit-content;
    margin: auto;
    border: solid;
    padding: 1em;
    background: white;
    color: black;
}