You sure did fine with moving the description part.
Now, your template is having a proprietary grid system built in, which you may want to utilise. Typically, it's simple: add "rt-grid-..." classes to the sections, e.g. like this:
class="hikashop_product_left_part rt-grid-5"
class="hikashop_product_right_part rt-grid-6"
Note that it should be "rt-grid-6" in both cases for a 50%/50% division, but that doesn't work well, probably because "rt-container" must be the class of the parent container somewhere. So, you'll need to ask your template provider for more on such details.
P.S.: Your "float: none;" is not destructive with the above mentioned classes, but you best remove it form the custom CSS again if you are using the rt-grid.