Use Flexbox for excerpt layout

css/excerpt.css

@@ -1,4 +1,7 @@
 .excerpt {
+  display: flex;
+  flex-flow: column nowrap;
+  flex-grow: 1;
   border-bottom: 1px solid var(--color-light-grey);
   margin-bottom: var(--space-sm);
   padding-bottom: var(--space-sm);
@@ -17,6 +20,10 @@
   margin-bottom: var(--space-xs);
 }
 
+.excerpt__body {
+  flex-grow: 1;
+}
+
 @media (--viewport-md) {
   .excerpt__head,
   .excerpt__body,

css/page.css

@@ -87,17 +87,14 @@
     grid-template-rows: 32px 162px 1fr;
   }
 
-  .page__content--2col {
-    display: grid;
-    grid-template-columns: 1fr 1fr;
-    grid-gap: var(--space-md);
-  }
-
-  .page__content-item {
+  .page__columns {
     display: flex;
+    flex-flow: row wrap;
   }
 
-  .page__content-item--full-width {
-    grid-column: 1 / -1;
+  .page__cell {
+    display: flex;
+    flex-flow: column nowrap;
+    flex: 1 0 50%;
   }
 }