diff --git a/README.md b/README.md
index f56ea1c95..07945a8e7 100644
--- a/README.md
+++ b/README.md
@@ -277,7 +277,7 @@ X. Exit testing.
 
 [implementation-specific expectations]: #implementation-specific-expectations
 
-Any option can also be applied to all future occurences of that type of failure
+Any option can also be applied to all future occurrences of that type of failure
 by adding `!` after it. For example, if you want to mark *all* failing specs as
 `:todo` for the current implementation you'd type `I!`.
 
diff --git a/spec/core_functions/meta/load_css/error/load.hrx b/spec/core_functions/meta/load_css/error/load.hrx
index c4f7fcaa1..37be4229e 100644
--- a/spec/core_functions/meta/load_css/error/load.hrx
+++ b/spec/core_functions/meta/load_css/error/load.hrx
@@ -34,3 +34,23 @@ Error: Module loop: input.scss is already being loaded.
   '
   _other.scss 2:1  load-css()
   input.scss 2:1   root stylesheet
+
+<===>
+================================================================================
+<===> top_level_include_declaration/input.scss
+@use "sass:meta";
+@include meta.load-css("upstream");
+
+<===> top_level_include_declaration/_upstream.scss
+@mixin a { b: c }
+@include a;
+
+<===> top_level_include_declaration/error
+Error: Declarations may only be used within style rules.
+  ,
+1 | @mixin a { b: c }
+  |            ^^^^^
+  '
+  _upstream.scss 1:12  a()
+  _upstream.scss 2:1   load-css()
+  input.scss 2:1       root stylesheet
diff --git a/spec/core_functions/meta/load_css/extend.hrx b/spec/core_functions/meta/load_css/extend.hrx
index 1cbddd0e1..b04889a63 100644
--- a/spec/core_functions/meta/load_css/extend.hrx
+++ b/spec/core_functions/meta/load_css/extend.hrx
@@ -104,3 +104,64 @@ a {
 .target, .extender {
   a: b;
 }
+
+<===>
+================================================================================
+<===> nested/README.md
+These are regression tests for https://github.com/sass/dart-sass/issues/2588.
+
+<===>
+================================================================================
+<===> nested/without_use/input.scss
+@use 'sass:meta';
+.a {
+  @include meta.load-css('upstream');
+}
+
+<===> nested/without_use/_upstream.scss
+@mixin b { c: d }
+@include b;
+
+<===> nested/without_use/output.css
+.a {
+  c: d;
+}
+
+<===> nested/without_use/warning
+DEPRECATION WARNING [import]: Sass @import rules are deprecated and will be removed in Dart Sass 3.0.0.
+More info and automated migrator: https://sass-lang.com/d/import
+  ,
+2 |   @import 'upstream';
+  |           ^^^^^^^^^^
+  '
+    input.scss 2:11  root stylesheet
+
+<===>
+================================================================================
+<===> nested/with_use/input.scss
+@use 'sass:meta';
+.a {
+  @include meta.load-css('midstream');
+}
+
+<===> nested/with_use/_midstream.scss
+@use 'upstream';
+@mixin b { c: d }
+@include b;
+
+<===> nested/with_use/_upstream.scss
+// Intentionally empty.
+
+<===> nested/with_use/output.css
+.a {
+  c: d;
+}
+
+<===> nested/with_use/warning
+DEPRECATION WARNING [import]: Sass @import rules are deprecated and will be removed in Dart Sass 3.0.0.
+More info and automated migrator: https://sass-lang.com/d/import
+  ,
+2 |   @import 'upstream';
+  |           ^^^^^^^^^^
+  '
+    input.scss 2:11  root stylesheet
diff --git a/spec/directives/import/nested.hrx b/spec/directives/import/nested.hrx
index b6baf321b..57dcb71e3 100644
--- a/spec/directives/import/nested.hrx
+++ b/spec/directives/import/nested.hrx
@@ -211,10 +211,10 @@ More info and automated migrator: https://sass-lang.com/d/import
 /* Y */
 
 <===> with_comment/_b.scss
-@import 'a'
+@import 'a';
 
 <===> with_comment/_c.scss
-@import 'a'
+@import 'a';
 
 <===> with_comment/output.css
 /* Y */
@@ -246,7 +246,7 @@ DEPRECATION WARNING [import]: Sass @import rules are deprecated and will be remo
 More info and automated migrator: https://sass-lang.com/d/import
 
   ,
-1 | @import 'a'
+1 | @import 'a';
   |         ^^^
   '
     _b.scss 1:9     @import
@@ -257,8 +257,114 @@ DEPRECATION WARNING [import]: Sass @import rules are deprecated and will be remo
 More info and automated migrator: https://sass-lang.com/d/import
 
   ,
-1 | @import 'a'
+1 | @import 'a';
   |         ^^^
   '
     _c.scss 1:9     @import
     input.scss 2:9  root stylesheet
+
+<===>
+================================================================================
+<===> top_level_include_declaration/README.md
+These are regression tests for https://github.com/sass/dart-sass/issues/2588.
+
+<===>
+================================================================================
+<===> top_level_include_declaration/without_use/input.scss
+.a {
+  @import 'upstream';
+}
+
+<===> top_level_include_declaration/without_use/_upstream.scss
+@mixin b { c: d }
+@include b;
+
+<===> top_level_include_declaration/without_use/output.css
+.a {
+  c: d;
+}
+
+<===> top_level_include_declaration/without_use/warning
+DEPRECATION WARNING [import]: Sass @import rules are deprecated and will be removed in Dart Sass 3.0.0.
+More info and automated migrator: https://sass-lang.com/d/import
+  ,
+2 |   @import 'upstream';
+  |           ^^^^^^^^^^
+  '
+    input.scss 2:11  root stylesheet
+
+<===>
+================================================================================
+<===> top_level_include_declaration/with_use/input.scss
+.a {
+  @import 'midstream';
+}
+
+<===> top_level_include_declaration/with_use/_midstream.scss
+@use 'upstream';
+@mixin b { c: d }
+@include b;
+
+<===> top_level_include_declaration/with_use/_upstream.scss
+// Intentionally empty.
+
+<===> top_level_include_declaration/with_use/output.css
+.a {
+  c: d;
+}
+
+<===> top_level_include_declaration/with_use/warning
+DEPRECATION WARNING [import]: Sass @import rules are deprecated and will be removed in Dart Sass 3.0.0.
+
+More info and automated migrator: https://sass-lang.com/d/import
+
+  ,
+2 |   @import 'midstream';
+  |           ^^^^^^^^^^^
+  '
+    input.scss 2:11  root stylesheet
+
+<===>
+================================================================================
+<===> top_level_include_declaration/with_use_two_levels_deep/input.scss
+.a {
+  @import 'midstream1';
+}
+
+<===> top_level_include_declaration/with_use_two_levels_deep/_midstream1.scss
+@import 'midstream2';
+
+<===> top_level_include_declaration/with_use_two_levels_deep/_midstream2.scss
+@use 'upstream';
+@mixin b { c: d }
+@include b;
+
+<===> top_level_include_declaration/with_use_two_levels_deep/_upstream.scss
+// Intentionally empty.
+
+<===> top_level_include_declaration/with_use_two_levels_deep/output.css
+.a {
+  c: d;
+}
+
+<===> top_level_include_declaration/with_use_two_levels_deep/warning
+DEPRECATION WARNING [import]: Sass @import rules are deprecated and will be removed in Dart Sass 3.0.0.
+
+More info and automated migrator: https://sass-lang.com/d/import
+
+  ,
+2 |   @import 'midstream1';
+  |           ^^^^^^^^^^^^
+  '
+    input.scss 2:11  root stylesheet
+
+DEPRECATION WARNING [import]: Sass @import rules are deprecated and will be removed in Dart Sass 3.0.0.
+
+More info and automated migrator: https://sass-lang.com/d/import
+
+  ,
+1 | @import 'midstream2';
+  |         ^^^^^^^^^^^^
+  '
+    _midstream1.scss 1:9  @import
+    input.scss 2:11       root stylesheet
diff --git a/spec/directives/use/error/load.hrx b/spec/directives/use/error/load.hrx
index d454ab282..90a90773d 100644
--- a/spec/directives/use/error/load.hrx
+++ b/spec/directives/use/error/load.hrx
@@ -328,3 +328,40 @@ Error: There's already a module with namespace "other".
   | ^^^^^^^^^^^^^^^^^^^^^^ new @use
   '
   input.scss 2:1  root stylesheet
+
+<===>
+================================================================================
+<===> top_level_include_declaration/upstream_mixin/input.scss
+@use "upstream";
+@include upstream.a;
+
+<===> top_level_include_declaration/upstream_mixin/_upstream.scss
+@mixin a { b: c }
+
+<===> top_level_include_declaration/upstream_mixin/error
+Error: Declarations may only be used within style rules.
+  ,
+1 | @mixin a { b: c }
+  |            ^^^^^
+  '
+  _upstream.scss 1:12  a()
+  input.scss 2:1       root stylesheet
+
+<===>
+================================================================================
+<===> top_level_include_declaration/input_mixin/input.scss
+@use 'upstream';
+@mixin a { b: c }
+@include a;
+
+<===> top_level_include_declaration/input_mixin/_upstream.scss
+// Intentionally empty.
+
+<===> top_level_include_declaration/input_mixin/error
+Error: Declarations may only be used within style rules.
+  ,
+2 | @mixin a { b: c }
+  |            ^^^^^
+  '
+  input.scss 2:12  a()
+  input.scss 3:1   root stylesheet