Lots of more advanced WordPress Themes these days comes with an extra css file called the custom stylesheet. You will find this file along the css stylsheet file when you open your Theme editor, providing of course, that your Theme has it included in the Theme file. Premium Themes like the Thesis Theme has this file built into the Theme for easy customizations.
The custom css file as the name suggest is for people who wants to change the look and feel of their Theme without having to change anything in the core css stylesheet. Thus if customizations have been done through the cutom css, and if the results are not satisfactory, users can simply delete whatever codes they have added in there and the Theme will revert back to it’s original look.
To change or add any extra styling in the custom css file, the magic word is dot custom (.custom). Placing this word in front of any stylesheet selectors will overwrite the styling attributes declared in the original stylesheet. For example, if the looks of your page layout is declared like this in your original sytlesheet,
#page { background-color: white; border: 1px solid #959596; text-align: left; }
and you want to change the look of your page, all you have to do is copy and paste those codes into your custom css and then add the magic word, .custom in front of the hash tag like this:
.custom #page { background-color: white; border: 1px solid #959596; text-align: left; }
After that you can change whatever values you want and if you do not like it, change again and again until you are happy. If not, just delete that line and it will revert back to the original look. You can also do the same if it is a class selector with the dot in front instead of the hash symbol.
It also works similarly of you want to add any new styles to your Theme.
