Improve UI Structure Consistency

src/styles.scss

@@ -29,21 +29,28 @@ strong {
   font-weight: 900;
 }
 
+h1, h2, h3 {
+  margin: 0;
+}
+
 h1 {
-  margin-bottom: 40px;
+  font-size: 48px;
   text-align: center;
 }
 
 h2 {
-  margin-top: 0;
-  margin-bottom: 20px;
-  font-size: 1.2rem;
+  font-size: 24px;
   color: oklch(0.5103 0 0); // #666
 }
 
+h3 {
+  font-size: 18px;
+}
+
 p {
-  margin-top: 15px;
+  margin-top: 0; margin-bottom: 0;
   font-weight: 500;
+  font-size: 16px;
 }
 
 .container {
@@ -65,7 +72,10 @@ p {
 }
 
 section.feature-block {
-  margin-bottom: 40px;
+  display: flex;
+  flex-direction: column;
+  gap: 12px;
+
   padding: 20px;
   border: 2px solid oklch(0 0 0 / 20%); // rgba(0, 0, 0, 0.2)
   border-radius: 8px;