convert to CSS variables

frontend/src/app/components/block-fees-graph/block-fees-graph.component.ts

@@ -214,7 +214,7 @@ export class BlockFeesGraphComponent implements OnInit {
           splitLine: {
             lineStyle: {
               type: 'dotted',
-              color: '#ffffff66',
+              color: 'var(--transparent-fg)',
               opacity: 0.25,
             }
           },
@@ -305,7 +305,7 @@ export class BlockFeesGraphComponent implements OnInit {
     const now = new Date();
     // @ts-ignore
     this.chartOptions.grid.bottom = 40;
-    this.chartOptions.backgroundColor = '#11131f';
+    this.chartOptions.backgroundColor = 'var(--active-bg)';
     this.chartInstance.setOption(this.chartOptions);
     download(this.chartInstance.getDataURL({
       pixelRatio: 2,