Switch dialog/popover to using place-self:dialog

See w3c/csswg-drafts#10258 for context.

Author: tabatkins

source

@@ -145205,19 +145205,16 @@ listing, plaintext, pre, xmp {
 dialog:not([open]) { display: none; }
 dialog {
   position: absolute;
-  inset-inline-start: 0; inset-inline-end: 0;
-  width: fit-content;
-  height: fit-content;
-  margin: auto;
+  justify-self: dialog;
   border: solid;
   padding: 1em;
   background-color: Canvas;
   color: CanvasText;
 }
 dialog:modal {
   position: fixed;
+  place-self: dialog;
   overflow: auto;
-  inset-block: 0;
   max-width: calc(100% - 6px - 2em);
   max-height: calc(100% - 6px - 2em);
 }
@@ -145235,10 +145232,7 @@ dialog:popover-open {
 
 [popover] {
   position: fixed;
-  inset: 0;
-  width: fit-content;
-  height: fit-content;
-  margin: auto;
+  place-self: dialog;
   border: solid;
   padding: 0.25em;
   overflow: auto;