[FIX] website: restore s_btn style

closes odoo/odoo#43689

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>

addons/website/views/snippets/s_btn.xml

@@ -7,4 +7,10 @@
     </div>
 </template>
 
+<template id="assets_snippet_s_btn_css_000" inherit_id="website.assets_frontend">
+    <xpath expr="//link[last()]" position="after">
+        <link rel="stylesheet" type="text/scss" href="/website/static/src/snippets/s_btn/000.scss"/>
+    </xpath>
+</template>
+
 </odoo>