Demo for Add Custom CSS
In order to see a live example please visit the following address and check the source code.
Notice that just before the end of the head section of the code you will see the following line.
/* HERE IS PLACED THE CUSTOM CSS CODE IN ORDER TO OVERRIDE EXISTING CSS STYLES. */
This comment is the content of the following custom CSS file which normally will contain the custom code.
In the code of the live page you will see something like the following.