Change fieldset's default padding to match the majority

WebKit/Chromium/EdgeHTML have 0.75em left/right padding and
0.625em bottom padding. Gecko has it the other way around.

Tests: web-platform-tests/wpt#12501.

Fixes #3921.

Author: zcorpan

source

@@ -112277,9 +112277,9 @@ fieldset {
   margin-inline-end: 2px;
   border: groove 2px ThreeDFace;
   padding-block-start: 0.35em;
-  padding-inline-end: 0.625em;
-  padding-block-end: 0.75em;
-  padding-inline-start: 0.625em;
+  padding-inline-end: 0.75em;
+  padding-block-end: 0.625em;
+  padding-inline-start: 0.75em;
   min-width: min-content;
 }