Fix OpenAPI HTML descriptions in darkmode

Currently when an OpenAPI specification contains HTML in the description fields
it is not rendered with the correct theme font colors making the description
unreadable in darkmode.

This change adds an additional selector to the style theme that correctly
selects the description block and ensures colors follows the theme.

Signed-off-by: Crevil <bjoern.soerensen@gmail.com>

.changeset/stale-needles-applaud.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-api-docs': patch
+---
+
+Set font colors correctly for descriptions containing HTML

plugins/api-docs/src/components/OpenApiDefinitionWidget/OpenApiDefinition.tsx

@@ -53,6 +53,7 @@ const useStyles = makeStyles(theme => ({
           .opblock-summary-operation-id,
           .opblock-summary-path,
           .opblock-summary-path__deprecated,
+          .opblock-description-wrapper,
           .opblock-external-docs-wrapper,
           .opblock-section-header .btn,
           .opblock-section-header>label,
@@ -66,7 +67,7 @@ const useStyles = makeStyles(theme => ({
         fontFamily: theme.typography.fontFamily,
         color: theme.palette.text.primary,
       },
-      [`& .opblock .opblock-section-header, 
+      [`& .opblock .opblock-section-header,
           .model-box,
           section.models .model-container`]: {
         background: theme.palette.background.default,
@@ -75,7 +76,7 @@ const useStyles = makeStyles(theme => ({
           .parameter__in`]: {
         color: theme.palette.text.disabled,
       },
-      [`& table.model, 
+      [`& table.model,
           .parameter__type,
           .model.model-title,
           .model-title,
@@ -91,7 +92,7 @@ const useStyles = makeStyles(theme => ({
       [`& .parameter__name.required:after`]: {
         color: theme.palette.warning.dark,
       },
-      [`& table.model, 
+      [`& table.model,
           table.model .model,
           .opblock-external-docs-wrapper`]: {
         fontSize: theme.typography.fontSize,
@@ -104,7 +105,7 @@ const useStyles = makeStyles(theme => ({
         color: theme.palette.text.hint,
         backgroundColor: theme.palette.background.paper,
       },
-      [`& .opblock-summary-method, 
+      [`& .opblock-summary-method,
           .info a`]: {
         fontFamily: theme.typography.fontFamily,
       },