fix empty slide (#659)

Author: alexandruradovici

slides/lectures/resources/mmio/slides.md

@@ -60,19 +60,19 @@ example for RP2
 
 <template #-3>
 
-<div style="background: white; padding: 5px" class="rounded">
+<div style="background-color: white; padding: 5px" class="rounded">
 
-![Bus](./internal_bus.svg)
+<img src="./internal_bus.svg">
 
 </div>
 
 </template>
 
 <template #0>
 
-<div style="background: white; padding: 5px" class="rounded">
+<div style="background-color: white; padding: 5px" class="rounded">
 
-![Bus](./bus.svg)
+<img src="./bus.svg">
 
 </div>