add center to ButtonExpand + misc fix

src/assets/scss/base/_root.scss

@@ -13,4 +13,5 @@ body,
 main {
   flex: 1;
   overflow-y: auto;
+  overflow-x: hidden;
 }

src/assets/scss/classes/_img-wrapper.scss

@@ -2,7 +2,7 @@
   display: inline-block;
   position: relative;
 
-  &:not(:hover) .btn-expand {
+  &.on-hover:not(:hover) .btn-expand {
     display: none;
   }
 
@@ -11,6 +11,12 @@
     top: 0;
     right: 0;
 
+    &.center {
+      top: 50%;
+      right: 50%;
+      transform: translate(50%, -50%)
+    }
+
     padding: 0;
     width: 75px;
     height: 70px;