convert to CSS variables

frontend/src/app/lightning/nodes-networks-chart/nodes-networks-chart.component.scss

@@ -98,7 +98,7 @@
     .card-text {
       font-size: 18px;
       span {
-        color: #ffffff66;
+        color: var(--transparent-fg);
         font-size: 12px;
       }
     }

frontend/src/app/lightning/nodes-networks-chart/nodes-networks-chart.component.ts

@@ -352,7 +352,7 @@ export class NodesNetworksChartComponent implements OnInit, OnChanges {
           splitLine: {
             lineStyle: {
               type: 'dotted',
-              color: '#ffffff66',
+              color: 'var(--transparent-fg)',
               opacity: 0.25,
             },
           },
@@ -375,7 +375,7 @@ export class NodesNetworksChartComponent implements OnInit, OnChanges {
           splitLine: {
             lineStyle: {
               type: 'dotted',
-              color: '#ffffff66',
+              color: 'var(--transparent-fg)',
               opacity: 0.25,
             },
           },
@@ -449,7 +449,7 @@ export class NodesNetworksChartComponent implements OnInit, OnChanges {
     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,