The elements in the content are in an order indicated in the elements menu in the editor, so that the first element on the list is at the top in the content.
The elements can cover each other either entirely or partially so that the element underneath may not be visible. You can move an element upwards in the content, and on top of other elements, by dragging its name higher on the element list.
Additionally, make sure that the element's visibility is not restricted because it has been hidden. If an element is hidden, there is a cross over the eye icon next to the element's name and the icon is shown on red. You can make the element visible again by pressing the icon.