fix(plugin-api-docs): Fix dark theme Swagger's clear button font color

Signed-off-by: Carlos Esteban Lopez <lcarlosesteb@vmware.com>

.changeset/orange-experts-hug.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-api-docs': patch
+---
+
+Fix dark theme Swagger's clear button font color.

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

@@ -25,6 +25,9 @@ const useStyles = makeStyles(theme => ({
       fontFamily: theme.typography.fontFamily,
       color: theme.palette.text.primary,
 
+      ['& .btn-clear']: {
+        color: theme.palette.text.primary,
+      },
       [`& .scheme-container`]: {
         backgroundColor: theme.palette.background.default,
       },