Remove all the rounded corners in Bootstrap (restore to the default corner)

* {
  border-radius: 0 !important;
}

 

* {
  -webkit-border-radius: 0 !important;
     -moz-border-radius: 0 !important;
          border-radius: 0 !important;
}

variables.less

@border-radius-base:        0px;
@border-radius-large:       0px;
@border-radius-small:       0px;

In bootstrap 4 if you are compiling it you can disable radius alltogether in the _custom.scss file:

$enable-rounded: false;

Source: http://stackoverflow.com/questions/9742166/getting-rid-of-all-the-rounded-corners-in-twitter-bootstrap