Feat (Discover): Update styles to be compatible with next theme (#4644)

* Feat (Discover): Update styles to be compatible with next theme

1. Change doc table source highlight to use standard color functions instead of transparency
2. Build KUI CSS for next themes in OUI, and conditionally load to ensure surrounding doc view styled correctly
3. Update histogram styles to follow design guidance and avoid theme-specific imports

Signed-off-by: Josh Romero <rmerqg@amazon.com>

* add changelog

Signed-off-by: Josh Romero <rmerqg@amazon.com>

---------

Signed-off-by: Josh Romero <rmerqg@amazon.com>

CHANGELOG.md

@@ -20,6 +20,7 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 - Enable theme-switching via Advanced Settings to preview the Next theme ([#4475](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/4475))
 - Optimize `augment-vis` saved obj searching by adding arg to saved obj client ([#4595](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/4595))
 - Add resource ID filtering in fetch `augment-vis` obj queries ([#4608](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/4608))
+- [Discover] Update styles to compatible with OUI `next` theme ([#4644](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/4644))
 
 ### 🐛 Bug Fixes
 

packages/osd-ui-framework/Gruntfile.js

@@ -74,6 +74,8 @@ module.exports = function (grunt) {
     Promise.all([
       uiFrameworkCompile('src/kui_light.scss', 'dist/kui_light.css'),
       uiFrameworkCompile('src/kui_dark.scss', 'dist/kui_dark.css'),
+      uiFrameworkCompile('src/kui_next_light.scss', 'dist/kui_next_light.css'),
+      uiFrameworkCompile('src/kui_next_dark.scss', 'dist/kui_next_dark.css'),
     ]).then(done);
   });