diff --git a/client/scss/generic/_generic.scss b/client/scss/generic/_generic.scss
deleted file mode 100644
index 441a18b24a..0000000000
--- a/client/scss/generic/_generic.scss
+++ /dev/null
@@ -1 +0,0 @@
-// generic styles go in this folder.
diff --git a/wagtail/admin/static_src/wagtailadmin/css/normalize.css b/client/scss/generic/_normalize.scss
similarity index 100%
rename from wagtail/admin/static_src/wagtailadmin/css/normalize.css
rename to client/scss/generic/_normalize.scss
diff --git a/wagtail/admin/static_src/wagtailadmin/scss/layouts/404.scss b/client/scss/layouts/_404.scss
similarity index 100%
rename from wagtail/admin/static_src/wagtailadmin/scss/layouts/404.scss
rename to client/scss/layouts/_404.scss
diff --git a/wagtail/admin/static_src/wagtailadmin/scss/layouts/account.scss b/client/scss/layouts/_account.scss
similarity index 100%
rename from wagtail/admin/static_src/wagtailadmin/scss/layouts/account.scss
rename to client/scss/layouts/_account.scss
diff --git a/wagtail/images/static_src/wagtailimages/scss/add-multiple.scss b/client/scss/layouts/_add-multiple.scss
similarity index 100%
rename from wagtail/images/static_src/wagtailimages/scss/add-multiple.scss
rename to client/scss/layouts/_add-multiple.scss
diff --git a/wagtail/images/static_src/wagtailimages/scss/chooser-duplicate-upload.scss b/client/scss/layouts/_chooser-duplicate-upload.scss
similarity index 100%
rename from wagtail/images/static_src/wagtailimages/scss/chooser-duplicate-upload.scss
rename to client/scss/layouts/_chooser-duplicate-upload.scss
diff --git a/wagtail/admin/static_src/wagtailadmin/scss/layouts/compare-revisions.scss b/client/scss/layouts/_compare-revisions.scss
similarity index 100%
rename from wagtail/admin/static_src/wagtailadmin/scss/layouts/compare-revisions.scss
rename to client/scss/layouts/_compare-revisions.scss
diff --git a/wagtail/images/static_src/wagtailimages/scss/focal-point-chooser.scss b/client/scss/layouts/_focal-point-chooser.scss
similarity index 100%
rename from wagtail/images/static_src/wagtailimages/scss/focal-point-chooser.scss
rename to client/scss/layouts/_focal-point-chooser.scss
diff --git a/wagtail/users/static_src/wagtailusers/scss/groups_edit.scss b/client/scss/layouts/_groups-edit.scss
similarity index 100%
rename from wagtail/users/static_src/wagtailusers/scss/groups_edit.scss
rename to client/scss/layouts/_groups-edit.scss
diff --git a/wagtail/admin/static_src/wagtailadmin/scss/layouts/home.scss b/client/scss/layouts/_home.scss
similarity index 100%
rename from wagtail/admin/static_src/wagtailadmin/scss/layouts/home.scss
rename to client/scss/layouts/_home.scss
diff --git a/wagtail/images/static_src/wagtailimages/scss/listing.scss b/client/scss/layouts/_listing.scss
similarity index 100%
rename from wagtail/images/static_src/wagtailimages/scss/listing.scss
rename to client/scss/layouts/_listing.scss
diff --git a/wagtail/admin/static_src/wagtailadmin/scss/layouts/login.scss b/client/scss/layouts/_login.scss
similarity index 100%
rename from wagtail/admin/static_src/wagtailadmin/scss/layouts/login.scss
rename to client/scss/layouts/_login.scss
diff --git a/wagtail/contrib/modeladmin/static_src/wagtailmodeladmin/scss/choose_parent_page.scss b/client/scss/layouts/_modeladmin-choose-parent-page.scss
similarity index 100%
rename from wagtail/contrib/modeladmin/static_src/wagtailmodeladmin/scss/choose_parent_page.scss
rename to client/scss/layouts/_modeladmin-choose-parent-page.scss
diff --git a/wagtail/contrib/modeladmin/static_src/wagtailmodeladmin/scss/index.scss b/client/scss/layouts/_modeladmin.scss
similarity index 100%
rename from wagtail/contrib/modeladmin/static_src/wagtailmodeladmin/scss/index.scss
rename to client/scss/layouts/_modeladmin.scss
diff --git a/wagtail/admin/static_src/wagtailadmin/scss/layouts/page-editor.scss b/client/scss/layouts/_page-editor.scss
similarity index 100%
rename from wagtail/admin/static_src/wagtailadmin/scss/layouts/page-editor.scss
rename to client/scss/layouts/_page-editor.scss
diff --git a/wagtail/contrib/redirects/static/wagtailredirects/css/index.css b/client/scss/layouts/_redirects.scss
similarity index 100%
rename from wagtail/contrib/redirects/static/wagtailredirects/css/index.css
rename to client/scss/layouts/_redirects.scss
diff --git a/wagtail/admin/static_src/wagtailadmin/scss/layouts/report.scss b/client/scss/layouts/_report.scss
similarity index 100%
rename from wagtail/admin/static_src/wagtailadmin/scss/layouts/report.scss
rename to client/scss/layouts/_report.scss
diff --git a/wagtail/admin/static_src/wagtailadmin/scss/layouts/workflow-edit.scss b/client/scss/layouts/_workflow-edit.scss
similarity index 100%
rename from wagtail/admin/static_src/wagtailadmin/scss/layouts/workflow-edit.scss
rename to client/scss/layouts/_workflow-edit.scss
diff --git a/wagtail/admin/static_src/wagtailadmin/scss/layouts/workflow-progress.scss b/client/scss/layouts/_workflow-progress.scss
similarity index 100%
rename from wagtail/admin/static_src/wagtailadmin/scss/layouts/workflow-progress.scss
rename to client/scss/layouts/_workflow-progress.scss
diff --git a/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/jquery-ui-1.10.3.verdant.css b/client/scss/vendor/jquery-ui-1.10.3.verdant.css
similarity index 100%
rename from wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/jquery-ui-1.10.3.verdant.css
rename to client/scss/vendor/jquery-ui-1.10.3.verdant.css
diff --git a/wagtail/images/static_src/wagtailimages/css/vendor/jquery.Jcrop.min.css b/client/scss/vendor/jquery.Jcrop.min.css
similarity index 100%
rename from wagtail/images/static_src/wagtailimages/css/vendor/jquery.Jcrop.min.css
rename to client/scss/vendor/jquery.Jcrop.min.css
diff --git a/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery.tagit.css b/client/scss/vendor/jquery.tagit.css
similarity index 100%
rename from wagtail/admin/static_src/wagtailadmin/css/vendor/jquery.tagit.css
rename to client/scss/vendor/jquery.tagit.css
diff --git a/wagtail/admin/static_src/wagtailadmin/css/vendor/tagit.ui-zendesk.css b/client/scss/vendor/tagit.ui-zendesk.css
similarity index 100%
rename from wagtail/admin/static_src/wagtailadmin/css/vendor/tagit.ui-zendesk.css
rename to client/scss/vendor/tagit.ui-zendesk.css
diff --git a/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/animated-overlay.gif b/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/animated-overlay.gif
deleted file mode 100755
index d441f75ebf..0000000000
Binary files a/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/animated-overlay.gif and /dev/null differ
diff --git a/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-bg_flat_0_aaaaaa_40x100.png b/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-bg_flat_0_aaaaaa_40x100.png
deleted file mode 100755
index 09c6bbb573..0000000000
Binary files a/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-bg_flat_0_aaaaaa_40x100.png and /dev/null differ
diff --git a/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-bg_flat_100_246060_40x100.png b/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-bg_flat_100_246060_40x100.png
deleted file mode 100755
index 5c58b1eeb8..0000000000
Binary files a/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-bg_flat_100_246060_40x100.png and /dev/null differ
diff --git a/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-bg_flat_100_49c0c1_40x100.png b/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-bg_flat_100_49c0c1_40x100.png
deleted file mode 100755
index 7a5c3b6427..0000000000
Binary files a/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-bg_flat_100_49c0c1_40x100.png and /dev/null differ
diff --git a/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-bg_flat_100_e8f8f9_40x100.png b/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-bg_flat_100_e8f8f9_40x100.png
deleted file mode 100755
index a23d87ee3b..0000000000
Binary files a/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-bg_flat_100_e8f8f9_40x100.png and /dev/null differ
diff --git a/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-bg_flat_100_f7474e_40x100.png b/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-bg_flat_100_f7474e_40x100.png
deleted file mode 100755
index f263007d4e..0000000000
Binary files a/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-bg_flat_100_f7474e_40x100.png and /dev/null differ
diff --git a/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-bg_flat_100_ffffff_40x100.png b/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-bg_flat_100_ffffff_40x100.png
deleted file mode 100755
index 6039d1d1c3..0000000000
Binary files a/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-bg_flat_100_ffffff_40x100.png and /dev/null differ
diff --git a/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-bg_flat_65_49c0c1_40x100.png b/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-bg_flat_65_49c0c1_40x100.png
deleted file mode 100755
index 7a5c3b6427..0000000000
Binary files a/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-bg_flat_65_49c0c1_40x100.png and /dev/null differ
diff --git a/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-icons_222222_256x240.png b/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-icons_222222_256x240.png
deleted file mode 100755
index c1cb1170c8..0000000000
Binary files a/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-icons_222222_256x240.png and /dev/null differ
diff --git a/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-icons_49c0c1_256x240.png b/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-icons_49c0c1_256x240.png
deleted file mode 100755
index fe9adc4d56..0000000000
Binary files a/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-icons_49c0c1_256x240.png and /dev/null differ
diff --git a/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-icons_555555_256x240.png b/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-icons_555555_256x240.png
deleted file mode 100755
index 5dcdcb41d3..0000000000
Binary files a/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-icons_555555_256x240.png and /dev/null differ
diff --git a/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-icons_ffffff_256x240.png b/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-icons_ffffff_256x240.png
deleted file mode 100755
index 4f624bb2b1..0000000000
Binary files a/wagtail/admin/static_src/wagtailadmin/css/vendor/jquery-ui/images/ui-icons_ffffff_256x240.png and /dev/null differ
diff --git a/wagtail/contrib/modeladmin/static_src/wagtailmodeladmin/scss/breadcrumbs_page.scss b/wagtail/contrib/modeladmin/static_src/wagtailmodeladmin/scss/breadcrumbs_page.scss
deleted file mode 100644
index 2c5155a80f..0000000000
--- a/wagtail/contrib/modeladmin/static_src/wagtailmodeladmin/scss/breadcrumbs_page.scss
+++ /dev/null
@@ -1,2 +0,0 @@
-@import '../../../../../../client/scss/settings';
-@import '../../../../../../client/scss/tools';
diff --git a/wagtail/documents/static_src/wagtaildocs/scss/add-multiple.scss b/wagtail/documents/static_src/wagtaildocs/scss/add-multiple.scss
deleted file mode 100644
index cc2e9bbeb6..0000000000
--- a/wagtail/documents/static_src/wagtaildocs/scss/add-multiple.scss
+++ /dev/null
@@ -1,91 +0,0 @@
-@import '../../../../../client/scss/settings';
-@import '../../../../../client/scss/tools';
-
-.replace-file-input {
-  display: inline-block;
-  position: relative;
-  overflow: hidden;
-  padding-bottom: 2px;
-
-  [type='file'] {
-    padding: 0;
-    opacity: 0;
-    position: absolute;
-    top: 0;
-    inset-inline-end: 0;
-    direction: ltr;
-    width: auto;
-    display: block;
-    font-size: 5em;
-
-    &:hover {
-      cursor: pointer;
-    }
-  }
-
-  &:hover {
-    cursor: pointer;
-
-    button {
-      background-color: $color-teal-darker;
-    }
-  }
-}
-
-.upload-list {
-  > li {
-    padding: 1em;
-  }
-
-  .left {
-    text-align: center;
-    word-break: break-all;
-  }
-
-  .preview {
-    width: 150px;
-    min-height: 150px;
-    display: block;
-    position: relative;
-    text-align: center;
-    max-width: 100%;
-    margin: auto;
-  }
-
-  .progress {
-    box-shadow: 0 0 5px 2px rgba(255, 255, 255, 0.4);
-    max-width: 100%;
-    z-index: 4;
-    margin-inline-start: 20%;
-    margin-inline-end: 20%;
-    width: 60%;
-  }
-
-  .status-msg {
-    display: none;
-  }
-
-  .upload-complete {
-    .progress {
-      opacity: 0;
-    }
-  }
-
-  .upload-success {
-    .status-msg.success {
-      display: block;
-    }
-  }
-
-  .upload-failure {
-    border-color: $color-red;
-
-    .preview {
-      display: none;
-    }
-
-    .status-msg.failure {
-      display: block;
-    }
-  }
-}
diff --git a/wagtail/images/static_src/wagtailimages/css/vendor/Jcrop.gif b/wagtail/images/static_src/wagtailimages/images/Jcrop.gif
similarity index 100%
rename from wagtail/images/static_src/wagtailimages/css/vendor/Jcrop.gif
rename to wagtail/images/static_src/wagtailimages/images/Jcrop.gif