Fixing the slider height

Hi

My blog is at Tales from Over the Horizon

I’m trying to set the height of the slider, but can’t seem to make anything work. It keeps on jumping around in height depending on the size of the photos. I would like them to be automatically sized when inserted into the slider.

One place I found said to download PC Custom CSS

and then paste

.flexslider .slides img {
height: 340px;
width: auto;

and change the height as you want.

I tried to fix it doing that.

To activate the PC Custom CSS plugin, it said to type the CSS into Custom CSS under Appearance. I did not know what to type. So I pasted the code written above. It did not work.

What am I supposed to put in the Custom CSS place and where am I supposed to put the code above.

OR if there is a different way of setting the slider height. Please tell me!

Thank you for your time