App: fix some CSS styling bugs related to Safari support

src/components/App/App.css

@@ -19,6 +19,10 @@ body {
   font-family: "Manrope";
 }
 
+h2 {
+  font-weight: 400;
+}
+
 pre,
 code {
   font-family: "IBM Plex Mono";

src/components/Header/Header.css

@@ -14,10 +14,15 @@ header img {
   flex-wrap: wrap;
   align-items: center;
   justify-content: flex-start;
-  gap: 56px;
+  /* gap: 56px; */
+  /* column-gap: 56px; */
   margin: 48px 0;
 }
 
+a.nav-link:not(:last-child) {
+  margin-right: 56px;
+}
+
 a.nav-link {
   text-decoration: none;
   position: relative;