html {
  -webkit-box-sizing: border-box;
  -moz-box-sizing: border-box;
  box-sizing: border-box;
}
*, *:before, *:after {
  -webkit-box-sizing: inherit;
  -moz-box-sizing: inherit;
  box-sizing: inherit;
}

.selector-for-some-widget {
  box-sizing: content-box;
}
/* With the above snippet, nested elements—including generated content via ::before and ::after—will all inherit the specified box-sizing for that .selector-for-some-widget. */

.back-to-top {
    position: fixed;
    bottom: 25px;
    right: 25px;
    display: none;
}