Let's take a quick look at some factors to consider when choosing and installing themes, just so that you'll be better informed.
A WordPress theme is actually a collection of files in a folder/directory. There are no special or unusual formats, just a few requirements for those files in the theme folder. The only requirements for a folder to be a valid WordPress theme are as follows:
It should have a
style.css
file and anindex.php
file.The
style.css
file must have the basic theme information in its first five lines.
There are a number of additional files that you'll find in most theme folders. They are as follows:
A
screenshot.png
file that is the little thumbnail that shows what the theme looks likeAn
images
folder where all images associated with the theme liveA variety of files that are used for different purposes (for example,
header.php
,footer.php
,page.php
,single.php
,archive.php
, and so on)