Will updating to new version of theme erase all my customization?

Depends. Some themes are updated to incorporate new WP features or to correct bugs. What you could do is download a copy of the newest version of Mystique to your local machine, extract the folder, change the theme’s folder name to Mystique2. Then edit the style.css file in a text editor (such as NotePad) and change:

Theme Name: Mystique

to

Theme Name: Mystique2

Finally upload the amended theme folder to wp-content/themes using FTP. That should allow you to keep both your old version and the new version. You can then compare and contrast them and, if you want, start porting over your CSS customisations to the new theme.

thanks!

Great advice – I’m such an amateur and I’m learning so much by using your forums.

– don’t modify any of the theme files, you will loose any changes you made when you update.
– if you need to make css customizations in Mystique, check the “User CSS” section from the theme settings. It’s much easier to use than the WordPress Editor anyway…

but if you really insist to modify the style.css file for some weird reason, do what esmi wrote (make a duplicate), then copy all the lines that you changed in the theme settings > User css page. This way you can still update safely, and you won’t have to repeat this everytime you update