refactor: Removes the CSS files from the Sankey Loop plugin (#19494)

* refactor: Removes the CSS files from the Sankey Loop plugin

* Gets opacity from the theme

superset-frontend/plugins/legacy-plugin-chart-sankey-loop/src/ReactSankeyLoop.jsx

@@ -0,0 +1,72 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+import React from 'react';
+import { reactify, styled } from '@superset-ui/core';
+import Component from './SankeyLoop';
+
+const ReactComponent = reactify(Component);
+
+const Sankey = ({ className, ...otherProps }) => (
+  <div className={className}>
+    <ReactComponent {...otherProps} />
+  </div>
+);
+
+export default styled(Sankey)`
+  ${({ theme }) => `
+    .superset-legacy-chart-sankey-loop .node rect {
+      cursor: move;
+      fill-opacity: ${theme.opacity.heavy};
+      shape-rendering: crispEdges;
+    }
+
+    .superset-legacy-chart-sankey-loop .node text {
+      pointer-events: none;
+      text-shadow: 0 1px 0 ${theme.colors.grayscale.light5};
+    }
+
+    .superset-legacy-chart-sankey-loop .link {
+      fill: none;
+      stroke: ${theme.colors.grayscale.dark2};
+      stroke-opacity: ${theme.opacity.light};
+    }
+
+    .superset-legacy-chart-sankey-loop .link:hover {
+      stroke-opacity: ${theme.opacity.mediumHeavy};
+    }
+
+    .superset-legacy-chart-sankey-loop .link path {
+      opacity: ${theme.opacity.mediumLight};
+      stroke-opacity: 0;
+    }
+
+    .superset-legacy-chart-sankey-loop .link:hover path {
+      opacity: ${theme.opacity.heavy};
+    }
+
+    .superset-legacy-chart-sankey-loop .link text {
+      fill: ${theme.colors.grayscale.base};
+      font-size: ${theme.gridUnit * 3}px;
+    }
+
+    .superset-legacy-chart-sankey-loop .link:hover text {
+      opacity: 1;
+    }
+ `}
+`;