Refactor layout and button styles

* Add single-column layout for forms
* Add optional nav/buttons to section headers

app/styles/_layout.scss

@@ -13,6 +13,21 @@ main {
       "stats"
       "contributions";
   }
+
+  &.center-column {
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+
+    section {
+      width: 600px;
+      max-width: 100%;
+
+      header {
+        text-align: center;
+      }
+    }
+  }
 }
 
 @media (min-width: 550px) {
@@ -39,11 +54,35 @@ main section {
   }
 
   header {
-    padding-bottom: 3rem;
-    text-align: center;
+    margin-bottom: 3rem;
+
+    &.with-nav {
+      display: grid;
+      grid-template-columns: auto 5rem;
+      grid-template-areas:
+        "title" "actions";
+
+      @include media-min(medium) {
+        grid-template-columns: auto 5rem 1.2rem;
+        grid-template-areas:
+          "title" "actions" "padding";
+      }
+    }
+
+    h2 {
+      display: inline-block;
+      // padding-left: 1.2rem;
+    }
+
+    nav {
+      display: flex;
+      flex-direction: row;
+      align-items: center;
+      justify-content: flex-end;
+    }
 
     @include media-max(small) {
-      padding-bottom: 2rem;
+      margin-bottom: 2rem;
     }
   }
 }