Is Default Bootstrap CSS Customized or Outdated?

I found out that the bootstrap css used in the Bootstrap Studio is apply stylings that is different than what I anticipated, because the style applied by bootstrap css are different than the one from, which I'm used for references while building my website.

Eg. When I include a button with .btn.btn-primary into my website, the css applied is the following:

.btn-primary {
  background-image:-webkit-linear-gradient(top,#337ab7 0,#265a88 100%);
  background-image:-o-linear-gradient(top,#337ab7 0,#265a88 100%);
  background-image:-webkit-gradient(linear,left top,left bottom,from(#337ab7),to(#265a88));
  background-image:linear-gradient(to bottom,#337ab7 0,#265a88 100%);
  filter:progid:DXImageTransform.Microsoft.gradient(startColorstr='#ff337ab7', endColorstr='#ff265a88', GradientType=0);

while I actually anticipated the bootstrap css to be as follows for my button:

.btn-primary {
    color: #fff;
    background-color: #337ab7;
    border-color: #2e6da4;

So, is there any reason of why there's difference in styling for bootstrap within the Bootstrap Studio? Or am I missing something?

Oops, never mind, apparently I need to switch to "Bootstrap without themes" in my settings. I actually prefer that the "Bootstrap without themes" as the default theme.

Good to know. Thank for the information.