is there any general or universal way to change Drupal's objects CSS? In some cases, when I install new themes, some regions\ blocks\buttons are too near to each other, and I need to start adding margins between them individually with css. This takes much time... 

Is there a way to automate this process? Is there some kind of a general\universal ID or class for all regions\blocks\buttons that I might be able to use to space all of regions\blocks\buttons "In one piece" and with much comfortability? It could also help me save time that could go on other things.
No. Of course there are default Drupal styles but there are no guarantees that whichever base theme you are working from hasn't overridden them.

The good news is that most popular base themes will implement classes that are universal to a particular type of output, like a row or a block. For instance, Foundation uses its own 'row' and 'column' but retains the core 'block' class.

Since you asked :), here is something you might do to add padding to columns in a Bootstrap subtheme:

.main-container &gt; .row &gt; section {padding: 1em;}


Note the '>' combinator. This refers to immediate descendents. 

&lt;div class="main-container"&gt;
  &lt;div class="row"&gt;
    &lt;section&gt;
      &lt;!-- this element will be our target since it's an immediate descendent of .row --&gt;
      &lt;section&gt;
        &lt;!-- this element is not --&gt;
      &lt;/section&gt;
    &lt;/section&gt;
  &lt;/div&gt;
&lt;/div&gt;


Note: If a selector is prefixed with '#' it is an id, and will only apply to one element. A class is prefixed with '.' and can apply to multiple elements. So all rows in bootstrap can be accessed with:

.row {padding: 1em;}