Merge branch 'master' of github.com:spotify/backstage into migrate-to-msw

* 'master' of github.com:spotify/backstage: (139 commits)
  Cleanup
  Update PinButton.test.tsx
  feat: update github insights plugin version (#2973)
  Ignore IntelliJ *.iml files (#2971)
  chore(deps): bump rollup-plugin-dts from 1.4.11 to 1.4.13
  fix the plugin card on plugins page
  align 'Add to Marketplace' button on plugins page
  fix the PluginGrid on mobiles sizes
  use getBy query instead of queryBy when asserting for elements present in document (#2951)
  Update PinButton.tsx
  Add test case for Progress component (#2953)
  fix the styling of footer copy on mobile
  add changeset
  handle the case where no entities are available to show
  core-api: work around issue with ApiRef export const declarations
  core-api: move utility api system implementation into apis/system
  Update docs regarding npm config ignore-scripts flag
  Another try
  Fix Core Features configuration id (#2948)
  Fix test?
  ...

plugins/scaffolder/src/components/ScaffolderPage/ScaffolderPage.tsx

@@ -22,7 +22,6 @@ import {
   Header,
   Lifecycle,
   Page,
-  pageTheme,
   Progress,
   SupportButton,
   useApi,
@@ -66,7 +65,7 @@ export const ScaffolderPage = () => {
   }, [error, errorApi]);
 
   return (
-    <Page theme={pageTheme.home}>
+    <Page themeId="home">
       <Header
         pageTitleOverride="Create a New Component"
         title={

plugins/scaffolder/src/components/TemplateCard/TemplateCard.tsx

@@ -13,8 +13,15 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-import { Button, pageTheme } from '@backstage/core';
-import { Card, Chip, makeStyles, Typography } from '@material-ui/core';
+import { Button } from '@backstage/core';
+import { BackstageTheme, pageTheme } from '@backstage/theme';
+import {
+  Card,
+  Chip,
+  makeStyles,
+  Typography,
+  useTheme,
+} from '@material-ui/core';
 import React from 'react';
 import { generatePath } from 'react-router-dom';
 import { templateRoute } from '../../routes';
@@ -56,7 +63,10 @@ export const TemplateCard = ({
   type,
   name,
 }: TemplateCardProps) => {
-  const theme = pageTheme[type] ?? pageTheme.other;
+  const backstageTheme = useTheme<BackstageTheme>();
+
+  const themeId = pageTheme[type] ? type : 'other';
+  const theme = backstageTheme.getPageTheme({ themeId });
   const classes = useStyles({ backgroundImage: theme.backgroundImage });
   const href = generatePath(templateRoute.path, { templateName: name });
 

plugins/scaffolder/src/components/TemplatePage/TemplatePage.tsx

@@ -22,7 +22,6 @@ import {
   Lifecycle,
   Page,
   useApi,
-  pageTheme,
 } from '@backstage/core';
 import { catalogApiRef } from '@backstage/plugin-catalog';
 import { LinearProgress } from '@material-ui/core';
@@ -145,7 +144,7 @@ export const TemplatePage = () => {
   }
 
   return (
-    <Page theme={pageTheme.home}>
+    <Page themeId="home">
       <Header
         pageTitleOverride="Create a new component"
         title={