Update custom_css file

Adding CSS for anchor-container (the anchor container will be added in the next PR)

assets/css/custom.css

@@ -1,3 +1,20 @@
 #page-header {
   padding-left: 8px;
 }
+
+.anchor-container {
+  background: #060a17;
+  bottom: 0;
+  display: flex;
+  font-weight: 600;
+  gap: 2rem;
+  padding: 4px;
+  place-content: baseline center;
+  position: fixed;
+  width: 100%;
+}
+
+.anchor-div {
+  display: flex;
+  flex-direction: row;
+}