✨ feat: introduce skins to customise the theme (#105)

sass/skins/evangelion.scss

@@ -0,0 +1,9 @@
+// Evangelion Unit-02.
+:root {
+    --primary-color: #d12e36;  // Contrast ratio: 5.05:1
+}
+
+// Evangelion Unit-01.
+[data-theme='dark'] {
+    --primary-color: #c09bd9;  // Contrast
+}