style.css

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: 'Poppins', sans-serif;
  font-size: 16px;
  color: #2c2c2c;
}
body a {
  color: inherit;
  text-decoration: none;
}

.header__btn {
  transition-property: all;
  transition-duration: 0.2s;
  transition-timing-function: linear;
  transition-delay: 0s;
  padding: 10px 20px;
  display: inline-block;
  margin-right: 10px;
  background-color: #fff;
  border: 1px solid #2c2c2c;
  border-radius: 3px;
  cursor: pointer;
  outline: none;
}
.header__btn:last-child {
  margin-right: 0;
}
.header__btn:hover, .header__btn.js-active {
  color: #fff;
  background-color: #2c2c2c;
}

.header {
  max-width: 600px;
  margin: 50px auto;
  text-align: center;
}

.header__title {
  margin-bottom: 30px;
  font-size: 2.1rem;
}

.content {
  width: 95%;
  margin: 0 auto 50px;
}

.content__title {
  margin-bottom: 40px;
  font-size: 20px;
  text-align: center;
}

.content__title--m-sm {
  margin-bottom: 10px;
}

.multisteps-form__progress {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(0, 1fr));
}

.multisteps-form__progress-btn {
  transition-property: all;
  transition-duration: 0.15s;
  transition-timing-function: linear;
  transition-delay: 0s;
  position: relative;
  padding-top: 20px;
  color: rgba(108, 117, 125, 0.7);
  text-indent: -9999px;
  border: none;
  background-color: transparent;
  outline: none !important;
  cursor: pointer;
}
@media (min-width: 500px) {
  .multisteps-form__progress-btn {
    text-indent: 0;
  }
}
.multisteps-form__progress-btn:before {
  position: absolute;
  top: 0;
  left: 50%;
  display: block;
  width: 13px;
  height: 13px;
  content: '';
  -webkit-transform: translateX(-50%);
          transform: translateX(-50%);
  transition: all 0.15s linear 0s, -webkit-transform 0.15s cubic-bezier(0.05, 1.09, 0.16, 1.4) 0s;
  transition: all 0.15s linear 0s, transform 0.15s cubic-bezier(0.05, 1.09, 0.16, 1.4) 0s;
  transition: all 0.15s linear 0s, transform 0.15s cubic-bezier(0.05, 1.09, 0.16, 1.4) 0s, -webkit-transform 0.15s cubic-bezier(0.05, 1.09, 0.16, 1.4) 0s;
  border: 2px solid currentColor;
  border-radius: 50%;
  background-color: #fff;
  box-sizing: border-box;
  z-index: 3;
}
.multisteps-form__progress-btn:after {
  position: absolute;
  top: 5px;
  left: calc(-50% - 13px / 2);
  transition-property: all;
  transition-duration: 0.15s;
  transition-timing-function: linear;
  transition-delay: 0s;
  display: block;
  width: 100%;
  height: 2px;
  content: '';
  background-color: currentColor;
  z-index: 1;
}
.multisteps-form__progress-btn:first-child:after {
  display: none;
}
.multisteps-form__progress-btn.js-active {
  color: #007bff;
}
.multisteps-form__progress-btn.js-active:before {
  -webkit-transform: translateX(-50%) scale(1.2);
          transform: translateX(-50%) scale(1.2);
  background-color: currentColor;
}

.multisteps-form__form {
  position: relative;
}

.multisteps-form__panel {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 0;
  opacity: 0;
  visibility: hidden;
}
.multisteps-form__panel.js-active {
  height: auto;
  opacity: 1;
  visibility: visible;
}
.multisteps-form__panel[data-animation="scaleOut"] {
  -webkit-transform: scale(1.1);
          transform: scale(1.1);
}
.multisteps-form__panel[data-animation="scaleOut"].js-active {
  transition-property: all;
  transition-duration: 0.2s;
  transition-timing-function: linear;
  transition-delay: 0s;
  -webkit-transform: scale(1);
          transform: scale(1);
}
.multisteps-form__panel[data-animation="slideHorz"] {
  left: 50px;
}
.multisteps-form__panel[data-animation="slideHorz"].js-active {
  transition-property: all;
  transition-duration: 0.25s;
  transition-timing-function: cubic-bezier(0.2, 1.13, 0.38, 1.43);
  transition-delay: 0s;
  left: 0;
}
.multisteps-form__panel[data-animation="slideVert"] {
  top: 30px;
}
.multisteps-form__panel[data-animation="slideVert"].js-active {
  transition-property: all;
  transition-duration: 0.2s;
  transition-timing-function: linear;
  transition-delay: 0s;
  top: 0;
}
.multisteps-form__panel[data-animation="fadeIn"].js-active {
  transition-property: all;
  transition-duration: 0.3s;
  transition-timing-function: linear;
  transition-delay: 0s;
}
.multisteps-form__panel[data-animation="scaleIn"] {
  -webkit-transform: scale(0.9);
          transform: scale(0.9);
}
.multisteps-form__panel[data-animation="scaleIn"].js-active {
  transition-property: all;
  transition-duration: 0.2s;
  transition-timing-function: linear;
  transition-delay: 0s;
  -webkit-transform: scale(1);
          transform: scale(1);
}