Fixup for https://phabricator.services.mozilla.com/D259290

Author: Loirooriol

style/traversal.rs

@@ -15,6 +15,7 @@ use crate::style_resolver::{PseudoElementResolution, StyleResolverForElement};
 use crate::stylist::RuleInclusion;
 use crate::traversal_flags::TraversalFlags;
 use selectors::matching::SelectorCaches;
+#[cfg(feature = "gecko")]
 use selectors::parser::PseudoElement as PseudoElementTrait;
 use smallvec::SmallVec;
 use std::collections::HashMap;

style/values/resolved/counters.rs

@@ -5,6 +5,7 @@
 //! Resolved values for counter properties
 
 use super::{Context, ToResolvedValue};
+#[cfg(feature = "gecko")]
 use selectors::parser::PseudoElement;
 use crate::values::computed;