/* set main elements to box-sizing border-box for more reliable box model calc */
body,
div,
nav,
article,
section,
main,
header,
footer,
input,
form,
table,
fieldset,
textarea,
ul,
li,
span {
  box-sizing: border-box;
}

/* for applying border-box to other elements on ad-hoc basis */
.border-box {
  box-sizing: border-box;
}