Fix layout of Oops! text on Learn 404 page

Use a consistent relative positioning container for the text, to avoid an issue where `:where(.wp-block-group.wp-block-group-is-layout-constrained) { position: relative }` is only sometimes applied.

See #155

source/wp-content/themes/wporg-parent-2021/sass/page/_404.scss

@@ -20,6 +20,8 @@ body.error404 {
 		}
 
 		.wporg-parent-oops-container {
+			position: relative;
+
 			> p {
 				display: none;
 			}
@@ -31,14 +33,14 @@ body.error404 {
 				z-index: -1;
 				position: absolute;
 				top: 22px;
-				left: -4.9vw;
+				left: -10vw;
 				font-family: var(--wp--preset--font-family--eb-garamond);
 				font-size: var(--oops-font-size);
 				line-height: var(--oops-font-size);
 				opacity: 0.4; // Make the overlaid text more readable.
 
 				@include break-small() {
-					top: calc(var(--oops-font-size) * -0.25);
+					top: calc(var(--oops-font-size) * -0.55);
 				}
 			}
 		}