/*まずはお決まりのボックスサイズ算出をborer-boxに */
*,
*:before,
*:after {
  -webkit-box-sizing: inherit;
  box-sizing: inherit;
}

html {
  -webkit-box-sizing: border-box;
  box-sizing: border-box;
  font-size: 62.5%;/*rem算出をしやすくするために*/
}

.btn,
a.btn,
button.btn {
  font-size: 1.6rem;
  font-weight: 700;
  line-height: 1.5;
  position: relative;
  display: inline-block;
  padding: 1rem 4rem;
  cursor: pointer;
  -webkit-user-select: none;
  -moz-user-select: none;
  -ms-user-select: none;
  user-select: none;
  -webkit-transition: all 0.3s;
  transition: all 0.3s;
  text-align: center;
  vertical-align: middle;
  text-decoration: none;
  letter-spacing: 0.1em;
  color: #212529;
  border-radius: 0.5rem;
}

a.btn-border {
  padding: 1.5rem 4rem;
  border: 3px solid #000;
  border-radius: 0;
  border-radius: 100vh;
  background: #fff;
}

a.btn-border:before {
  position: absolute;
  top: 2px;
  left: 2px;
  width: calc(100% - 4px);
  height: calc(100% - 4px);
  content: '';
  -webkit-transition: all .3s;
  transition: all .3s;
  border: 3px dotted #000;
  border-radius: 100vh;
}

a.btn-border:hover:before {
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
}