style: fix button size

set button height with vh and not %

src/components/quiz/modalButton/modalButton.css

 .modal-button-left {
     width: 100%;
-    height: 100%;
+    height: 10vh;
     border-radius: 12px;
     border: solid 5px #508bff;
     background-color: white;
@@ -30,7 +30,7 @@
 
 .modal-button-right {
     width: 100%;
-    height: 100%;
+    height: 10vh;
     border-radius: 12px;
     background-color: #2b73fd;
     font-weight: bold;