Normalize and improve font sizes

This commit standardizes font sizes across components for a uniform
look. The icon sizes, font weights and line heights are also adjusted
accordingly for better standardization and simplicity.

- Introduce variables for standard font sizes, enhancing
  maintainability.
- Remove explicit pixel values, replaced with scalable units based on
  root size.
- Remove workaround for line-height adoptation of bigger font-size.
- Use consistent small font-size for the code area.
- Adjust checkbox tick to scale with font size.

src/presentation/components/Shared/Modal/ModalDialog.vue

@@ -74,7 +74,7 @@ export default defineComponent({
   .dialog__close-button {
     color: $color-primary-dark;
     width: auto;
-    font-size: 1.5em;
+    font-size: $font-size-large;
     margin-right: 0.25em;
     align-self: flex-start;
   }