convert to CSS variables

frontend/src/app/lightning/node/node-preview.component.scss

@@ -32,7 +32,7 @@
   min-height: 408px;
   max-height: 408px;
   padding: 0;
-  background: #181b2d;
+  background: var(--stat-box-bg);
   overflow: hidden;
   margin-top: 6px;
 }

frontend/src/app/lightning/node/node.component.html

@@ -1,7 +1,7 @@
 <div class="container-xl" *ngIf="(node$ | async) as node; else skeletonLoader">
 
   <ng-container *ngIf="!error">
-    <h5 class="mb-0" style="color: #ffffff66" i18n="lightning.node">Lightning node</h5>
+    <h5 class="mb-0" style="color: var(--transparent-fg)" i18n="lightning.node">Lightning node</h5>
     <div class="title-container mb-2">
       <div class="d-flex justify-content-between align-items-center">
         <h1 class="mb-0 text-truncate">{{ node.alias }}</h1>
@@ -303,7 +303,7 @@
 
 <ng-template #skeletonLoader>
   <div class="container-xl">
-    <h5 class="mb-0" style="color: #ffffff66" i18n="lightning.node">Lightning node</h5>
+    <h5 class="mb-0" style="color: var(--transparent-fg)" i18n="lightning.node">Lightning node</h5>
     <div class="title-container mb-2">
       <h1 class="mb-0"><span class="skeleton-loader" style="width: 250px; height: 36px; margin-top: 5px; margin-bottom: 5px;"></span></h1>
       <span class="tx-link">

frontend/src/app/lightning/node/node.component.scss

@@ -89,7 +89,7 @@ app-fiat {
 
   .tlv-type {
     font-size: 12px;
-    color: #ffffff66;
+    color: var(--transparent-fg);
   }
 
   .tlv-payload {