Don't worry. It isn't that complicated. I just wanted to give as much detail as I could.

This mod will change your back to top button from a rectangle to a circle. It will have an inital opacity that is more on the transparent end, but still visible. It has an on hover opacity that becomes more solid when you hover over the button with your mouse. The "background-color" can be changed to suit your needs by edditing the modified css file. I've also added an up arrow image with a transparent background. This allows you to see the black up arrow, and whatever color you set the background-color to. I used gimp, a free photo editing software, to set the transparent background. I didn't remove any of the other css that was originally there. I just changed some, and added more to acheive this look. The other file I changed was the admin php file. I just set the text field's "required" line from true to false. This made it possible to have, or not have text on the button.
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!!!Make a copy of your original settings before starting!!! Just copy everything, and paste it into notepad. This is just in case you ever want to go back to your originl settings, or if something goes wrong. Also make another copy after your done. If the plugin is ever updated the setting will be overwritten by the update.
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Gimp
If you want to create your own image. I highly recommend this software. It's free, and has a ton of functionality. There is a youtube video on how to do the transparent background. The best to work with are solid white backgrounds because what you are doing is selecting the background, and removing it.
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The background-image "this is in the css file "oxwall/ow_plugins/back2top/static/css"
I have also attached the up_arrow.png image that I made. NOTE: when you open the up arrow image attachment. Right click on the image, and choose "save as" from the drop down list. If you just copy it, the image won't display correctly. "Save as" keeps the transparancy. Name the image as up_arrow.png. You need to upload this image to the css folder "oxwall/ow_plugins/back2top/static/css" in cpanel. 
I found that 35x35px is a good size to center the image on the button. at least for the up arrow that I used. The image needs to be in the same folder as the css file.

background-image:url("up_arrow.png")!important;
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css
Copy the css file that I have included, and replace the existing css file. "oxwall/ow_plugins/back2top/static/css"
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admin.php
"oxwall/ow_plugins/back2top/controllers/admin.php" On line 51 "$element->setRequired(true);" Set this to false. This will make text on your button optional instead of requred. Note this is the first place you will see this line. it is also in the other form elements below it, but this is for the text field.
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The background=color "this is in the css file oxwall/ow_plugins/back2top/static/css"
I have it set to silver, but you can change that to whatever fits your site the best. If you use an image with a solid background, you won't see this color.

background-color:silver !important;
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Remember, as always, when you are done. Set dev mode to true "oxwall/includes/config.php" at the bottom of the page set dev to true. go to your site, and refresh the page. You should see your new modern go to top button. Set dev mode back to false, and your done.

Short instruction
1. Make a back up copy of the original css file incase you make a mistake.
2. open the up_arrow.png attachment. right click and choose "save as".
 a. In the "save as" box. Name the file up_arrow.png.
3. upload the up_arrow.png image to the css folder.
4. Open the css modification attachment copy it, and replace all of the existing css in the "oxwall/ow_plugins/back2top/static/css/BackToTop.jquery.css" file.
5. go to "oxwall/ow_plugins/back2top/controllers/admin.php" file. edit it to set the required text field from "true" to "false"
6. set dev mode to true, go to your site, and refresh the page. then set dev mode back to false.
6. your done, and you have a cool looking back to top button.