CSS Checkpoint

- Add the system_css template
- Name the CSS files in the css directory with a numeric prefix so they sort by
  priority.

assets/css/099_page_summary.css

@@ -0,0 +1,25 @@
+/**************************
+ # COMPONENT: PAGE SUMMARY
+ **************************/
+
+.summary {
+  &:not(:last-child) {
+    margin-block-end: var(--space-l);
+  }
+
+  .summary__post-title {
+    margin-block: 0 var(--space-xs);
+  }
+
+  .summary__post-subtitle {
+    font-weight: 500;
+  }
+
+  .summary__content {
+    margin-block-end: var(--space-m);
+  }
+
+  :is(.summary__post-title, .summary__post-subtitle):last-child {
+    margin-block-end: var(--space-m);
+  }
+}