Use css variables.

styles/index.css

@@ -1,7 +1,7 @@
 html,
 body {
   font-family: Inter, -apple-system, BlinkMacSystemFont, sans-serif;
-  font-size: 16px;
+  font-size: var(--font-size-normal);
   font-weight: 400;
   line-height: 1.8;
   padding: 0;
@@ -9,8 +9,8 @@ body {
   width: 100%;
   height: 100%;
   box-sizing: border-box;
-  color: #2c2c2c;
-  background: #fafafa;
+  color: var(--gray900);
+  background: var(--gray75);
 }
 
 *,
@@ -19,6 +19,10 @@ body {
   box-sizing: inherit;
 }
 
+h2 {
+  font-weight: 400;
+}
+
 #__next {
   display: flex;
   flex-direction: column;
@@ -35,12 +39,7 @@ select {
 a,
 a:active,
 a:visited {
-  color: #2680eb;
-}
-
-header a {
-  color: #2c2c2c !important;
-  text-decoration: none;
+  color: var(--primary400);
 }
 
 form label {
@@ -48,13 +47,19 @@ form label {
   min-width: 100px;
 }
 
-form input {
+form input,
+form textarea {
+  padding: 4px 8px;
   margin-right: 10px;
+  margin-bottom: 20px;
+  border: 1px solid var(--gray500);
+  border-radius: 4px;
+  outline: none;
 }
 
 select {
   padding: 4px 8px;
-  border: 1px solid #b3b3b3;
+  border: 1px solid var(--gray500);
   border-radius: 4px;
 }
 

styles/variables.css

@@ -0,0 +1,29 @@
+:root {
+  --gray50: #ffffff;
+  --gray75: #fafafa;
+  --gray100: #f5f5f5;
+  --gray200: #eaeaea;
+  --gray300: #e1e1e1;
+  --gray400: #cacaca;
+  --gray500: #b3b3b3;
+  --gray600: #8e8e8e;
+  --gray6700: #6e6e6e;
+  --gray800: #4b4b4b;
+  --gray900: #2c2c2c;
+
+  --primary400: #2680eb;
+  --primary500: #1473e6;
+  --primary600: #0d66d0;
+  --primary700: #095aba;
+
+  --font-size-xlarge: 36px;
+  --font-size-large: 24px;
+  --font-size-normal: 16px;
+  --font-size-small: 14px;
+  --font-size-xsmall: 12px;
+
+  --grid-size-small: 576px;
+  --grid-size-medium: 768px;
+  --grid-size-large: 992px;
+  --grid-size-xlarge: 1140px;
+}