chore: Use IDs instead of classes for nav and footer; change name to site-nav/footer

sass/_footer.scss

@@ -1,4 +1,4 @@
-.footer {
+#site-footer {
   text-align: center;
   padding: 3rem 0 3rem;
   font-size: 1rem;

sass/_nav.scss

@@ -1,4 +1,4 @@
-#header {
+#site-nav {
   -webkit-backdrop-filter: saturate(180%) blur(20px);
   backdrop-filter: saturate(180%) blur(20px);
   background-color: var(--nav-bg);

templates/includes/footer.html

@@ -1,4 +1,4 @@
-<footer class="footer">
+<footer id="site-footer">
   {% if config.extra.footer.show_copyright %}
     <p title="Last built at {{ now() | date(format='%F %R %Z') }}">&copy; {{ config.title }}, {{ now() | date(format="%Y") }}</p>
   {% endif %}

templates/includes/nav.html

@@ -1,4 +1,4 @@
-<header id="header">
+<header id="site-nav">
   <nav>
     <a id="title" href="{{ get_url(path='') }}">
       {% if config.extra.nav.icons %}