Fix fullscreen modal left margins

src/definitions/modules/modal.less

@@ -335,9 +335,12 @@
 
 .ui.fullscreen.modal {
   width: @fullScreenWidth !important;
-  left: 0% !important;
+  left: @fullScreenOffset !important;
   margin: @fullScreenMargin;
 }
+.ui.fullscreen.scrolling.modal {
+  left: 0em !important;
+}
 .ui.fullscreen.modal > .header {
   padding-right: @closeHitbox;
 }

src/themes/default/modules/modal.variables

@@ -90,6 +90,7 @@
 @widescreenMonitorMargin: 0em 0em 0em -(@widescreenMonitorWidth / 2);
 
 @fullScreenWidth: 95%;
+@fullScreenOffset: (100% - @fullScreenWidth) / 2;
 @fullScreenMargin: 1em auto;
 
 @fullScreenMobileWidth: auto;