Change button style

I want to change the style of the buttons, but it seems not all changes can be made.

I was inspecting 'My profile' button as an example, in common.css I can make changes in .bx-btn. But still there are changes to the button I cannot do, like deleting the borders of the button. 

 user agent stylesheet

input[type="button"],input[type="submit"], input[type="reset"],input[type="file"]::-webkit-file-upload-button, button {

1. -webkit-box-align:center;
2. text-align:center;
3. cursor:default;
4. color:buttontext;
5. padding:2px 6px 3px;
6. border:2px outset buttonface;
7. border-image:initial;
8. background-color:buttonface;
9. box-sizing:border-box;

Where do I make changes for the following? 

The easiest way to see what CSS is controlling what is to use a browser inspection tool.  For FF, I use firebug over the built in one; however, FF and Chrome have one built into the browser.  To use this tool you need to turn off CSS caching in the admin section and then clear caches and reload the page.  You would right click and choose inspect element.  Now you will see what CSS is controlling what; you would look for the css file; and it will even tell you the line number, that is controlling the element styling.  The strike-through means that your CSS property is being overriden by another CSS so you need to search to see where and make your changes in that style entry.

 I

 I am using Chrome developer tools for this one. I made changes to the button to the in the common.css file, but to remove borders I need to edit some other css file, but I cannot find it because instead of location and name of the needed file it shows 'user agent stylesheet' and I cannot apply any changes to it even in browser.

I also wanted to edit some other parts of the site and have faced the same agent.

Maybe it is overriden by jQuert stylesheet? If so, how can I apply changes to it?