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/TheSearchBar.vue

@@ -113,7 +113,7 @@ export default defineComponent({
   outline: none;
   color: $color-primary;
   font-family: $font-normal;
-  font-size:1em;
+  font-size: $font-size-normal;
   &:focus {
     color: $color-primary-darker;
   }
@@ -127,7 +127,7 @@ export default defineComponent({
   text-align: center;
   color: $color-on-primary;
   border-radius: 0 5px 5px 0;
-  font-size: 20px;
+  font-size: $font-size-large;
   padding:5px;
 }
 </style>