Any value set using % will change as the size of browser window changes: the bigger the browser, the bigger the padding will come.
If you want your design to scale well with different font sizes, then you use ems. So if users increase their browsers font sizes, then sizes set in ems will also increase accordignly.
Using px is for precise design with graphical elements that line up exactly, regardless of browser window size or font setting.
By the way, i checked your source code and you got few errors.
For the Cherry Art, when using <span> dont use "id" use "class" instead.
<p><span id="cherry">CHERRY ART</span> produces a wide range of prints…
For all the <spans id=""> change the id to class <span class="">