fix: unavailable --prime css variable (sveltejs#478)

Author: mateusabelli

src/routes/tutorial/[slug]/Menu.svelte

@@ -310,7 +310,7 @@
 
 	li[aria-current='page'] a,
 	li[aria-current='step']:not(.expanded) > button {
-		color: var(--prime);
+		color: var(--sk-theme-1);
 	}
 
 	li img {

src/routes/tutorial/[slug]/Sidebar.svelte

@@ -208,7 +208,7 @@
 
 	.modal-contents button {
 		display: block;
-		background: var(--prime);
+		background-color: var(--sk-theme-1);
 		color: white;
 		padding: 1rem;
 		width: 10em;