1. A non-transitory computer readable medium storing instructions that are executable by a processing device for causing the processing device to perform operations comprising: providing for display in a graphical user interface a first stack element corresponding to a first data item, the first stack element having a first display aspect ratio, the first display aspect ratio being determined based on an aspect ratio of the first data item; providing for display in the graphical user interface a second stack element corresponding to a second data item, wherein the second stack element comprises an indicium having a second display aspect ratio that is different from the first display aspect ratio, where the second display aspect ratio is determined based on an aspect ratio of the second data item; normalizing the second stack element by adding one or more borders to surround the indicium, wherein corresponding areas of the added borders are determined such that the normalized second stack element has the first display aspect ratio, where the second display aspect ratio of the indicium is preserved; and providing for display in the graphical user interface a stack item, the stack item including the first stack element and the normalized second stack element.