Resolve "Implement basic functionality"

Closes #1 (closed) Closes #2 (closed) Closes #3 (closed) Closes #4 (closed) Closes #5 (closed) Closes #6 (closed)

example/src/App.vue

@@ -62,6 +62,9 @@ import NumberCounter from "./components/NumberCounter.vue";
         <template #item="item">
           <number-counter v-model="item.data.num"></number-counter>
         </template>
+        <template #highlight>
+          <div ref="highlight" class="custom-highlight">Das hier ist das Highlight</div>
+        </template>
       </drag-grid>
       <span>← Drag here please →</span>
       <drag-grid v-model="counters2" :cols="3" :rows="2" context="counter">
@@ -293,6 +296,15 @@ export default {
   justify-content: space-between;
 }
 
+.custom-highlight {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  background: aquamarine;
+  width: 100%;
+  height: 100%;
+}
+
 .bordered {
   border: 2px solid grey;
 }