I used Firebug. This screencast might help.

Very nice.
Thank you for taking the trouble with the screencast.

Following this, I made an attempt to debug the issue of being unable to change the font size of the disclaimer content. In Firebug I clicked the element locator on the top left side, then clicked inside the page on the disclaimer content, then clicked on 'computed' in the top right part of the screen.
The font size reads 12px. The line that I put in on ATO > Add HTML/CSS Inserts is:
font-size: 32px; !important;

Why is the font size not responding to my changes?

~ Obi

To change the font size for the disclaimer you need to add the following to ATO>Add HTML/CSS Inserts>CSS Inserts

#disclaimer h3 {
font-size: 32px !important;
}

#disclaimer h3 is the header, with which I don't have a problem - I can change the font size there.
The change doesn't work for the content of the disclaimer:

/* Styling the disclaimer content */
#disclaimer {
background-color: #00ff00;
color: #ff0000;
font-size: 32px; !important;  /* this line shows no effect */
font-family: Tahoma serif;
}

~ Obi

For the text you could use

.textwidget

for the selector but that could affect other widgets so to limit it to the disclaimer area use

#disclaimer .textwidget

It works.

Tell me if I get it right;
In Firebug, clicking on the disclaimer content and then looking on the righthand side window under the Style tab - seeing that div.textwidget is the last selector in the inheritance chain . . .
Was that how you found .textwidget to be the right selector ?

I don't understand why is it that under #disclaimer I can change the color of the text as well as the background color,
but not the text size . . . unless it's some sort of a bug of course.

~ Obi

It has to do with the cascading part of CSS.

Thank you so much for your time and patience.
You have helped me a great deal.

~ Obi