If you find yourself in a situation where two images are overlapping each other, but the one you want on top is currently on the bottom, add the following code in your CSS:

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position: relative;
z-index: 5;

This code has to be applied to where both images are being called. For example, you would put z-index: 5; for the first one and z-index: 4; for the second image. The higher z-index number will be on top. This works great for overlaying transparent images over banners and such.