fix lint error

src/css/toc.css

+/* stylelint-disable-next-line property-no-unknown */
+
 .toc-menu {
   color: var(--toc-font-color);
   margin-top: 2.5rem;
@@ -280,19 +282,22 @@
 
 @keyframes l5 {
   0% {
-    box-shadow: 15px 0 var(--color-bwg-main), -15px 0 #0072CE20;
+    box-shadow: 15px 0 var(--color-bwg-main), -15px 0 var(--color-bwg-20);
     background: var(--color-bwg-main);
   }
+
   33% {
-    box-shadow: 15px 0 var(--color-bwg-main), -15px 0 #0072CE20;
-    background: #0072CE20;
+    box-shadow: 15px 0 var(--color-bwg-main), -15px 0 var(--color-bwg-20);
+    background: var(--color-bwg-20);
   }
+
   66% {
-    box-shadow: 15px 0 #0072CE20, -15px 0 var(--color-bwg-main);
-    background: #0072CE20;
+    box-shadow: 15px 0 var(--color-bwg-20), -15px 0 var(--color-bwg-main);
+    background: var(--color-bwg-20);
   }
+
   100% {
-    box-shadow: 15px 0 #0072CE20, -15px 0 var(--color-bwg-main);
+    box-shadow: 15px 0 var(--color-bwg-20), -15px 0 var(--color-bwg-main);
     background: var(--color-bwg-main);
   }
 }

src/css/vars.css

 :root {
   /* colors */
   --color-bwg-main: #0072ce;
+  --color-bwg-20: #0072ce20;
   --color-white: #fff;
   --color-smoke-10: #fefefe;
   --color-smoke-30: #fafafa;