Move default style for <dialog> to html.css

Source/core/css/html.css

Index: Source/core/css/html.css
diff --git a/Source/core/css/html.css b/Source/core/css/html.css
index 17f7402738542e4f9886cbb4704e53b461c51cd7..39b38d93c214b1302a60ab424b827335d875c0d6 100644
--- a/Source/core/css/html.css
+++ b/Source/core/css/html.css
@@ -1057,6 +1057,32 @@ textarea[dir=auto i] {
     unicode-bidi: -webkit-plaintext;
 }
 
+dialog:not([open]) {
+    display: none
+}
+
+dialog {
+    position: absolute;
+    left: 0;
+    right: 0;
+    width: -webkit-fit-content;
+    height: -webkit-fit-content;
+    margin: auto;
+    border: solid;
+    padding: 1em;
+    background: white;
+    color: black
+}
+
+dialog::backdrop {
+    position: fixed;
+    top: 0;
+    right: 0;
+    bottom: 0;
+    left: 0;
+    background: rgba(0,0,0,0.1)
+}
+
 /* page */
 
 @page {