Board Thread:Support Requests - Designing Your Wiki/@comment-9557431-20180203003723/@comment-168424-20180203021612

Did you try clicking the "tile" checkbox in Theme Designer?

What is the "correct file size"? Remember, how big the file is means nothing for how much space it actually takes up.

You can use programs like GIMP to save a JPEG at varying levels of quality to make even large dimension images take up less disk space.