2D elements start out being displayed by draw order. As you place elements in a file one on top of another that will be how they continue to be displayed. If you want to change this order there are several ways to do this.
Elements as drawn in file.
Select the element (i.e.Pattern), use Edit/Bring to Front.
Pattern is now on top.
Select an element (i.e. Single Green Line), select Element Information (ID), look for Priority, Set a priority specifically for that one element.
One Green Line is now on top.
In Level Manager setting a Priority will change the entire level display order. All elements drawn on the level are changed.
Set Fill to be behind all, Set Lines to be on top of all.
Make sure Level Priority column is turned on in Level Manager. Right Click in Name box to check on Priority.
You will not find Priority listed in a 3D file. 3D files are based on the Z depth Elevation of Elements. If all of your elements are drawn to a specific elevation your display is shown based on those elevations. You highest elements being on top.
If you are in a file that was originally a 2D file saved to 3D or a 3D file drawn as 2D with all elements at zero elevation you need to move the elements. You will want to manually move elements up or down in elevation to have them display correctly.
How to order reference attachments