main {
  overflow: hidden;
  padding-top: 100px;
}

.hero-section {
  min-height: 60vh;
}

.sub-header {
  font-size: 2.4em;
  position: relative;
}

.sub-header::after {
  content: "";
  background-color: transparent;
  width: 15vw;
  height: 15vw;
  border-radius: 50%;
  border: 5px solid var(--green);
  position: absolute;
  top: 0;
  left: 5vw;
  z-index: -1;
}

.sub-header::before {
  content: "";
  background-color: transparent;
  width: 40px;
  height: 40px;
  border-radius: 50%;
  border: 5px solid var(--green);
  position: absolute;
  bottom: 20px;
  right: 30px;
  z-index: -1;
}

/* 
  spine
 */

.spine-part {
  margin: 40px;
  margin-bottom: 150px;
  position: relative;
}

.spine-circles {
  position: absolute;
  top: -100px;
  left: -70px;
  display: flex;
  flex-direction: column;
  gap: 1em;
}

.spine-circle {
  background-color: var(--green);
  width: 60px;
  height: 60px;
  border-radius: 50%;
}

.spine-circle:nth-child(2) {
  background-color: var(--blue);
  width: 80px;
  height: 80px;
  border-radius: 50%;
}

.spine-part:nth-child(even) .spine-circles {
  left: inherit;
  right: -70px;
  transform: rotateZ(180deg);
}

.spine-part:nth-child(even) .spine-header h2 {
  text-align: end;
  padding-right: 20px;
}

.spine-text {
  background-color: var(--blue);
  border-radius: 30px;
}

.spine-header h2 {
  font-size: 2em;
  padding-left: 20px;
}

.spine-text {
  padding: 25px;
}

.spine-text p {
  color: var(--bg);
}

/* 
  big spine
 */

.spine-big {
  display: none;
}

.return-btn-container {
  background-color: var(--bg);
  height: 200px;
  width: 200px;
  overflow: hidden;
  display: flex;
  text-align: center;
  justify-content: center;
  align-items: center;
  border-radius: 50%;
  margin: 60px auto 80px auto;
  border: 3px solid var(--green);
  transition: all 0.4s ease;
}

#bottom-return-btn {
  color: var(--green);
  font-size: 2.2em;
  padding: 100px 40px;
  transition: all 0.4s ease;
}

#bottom-return-btn:hover {
  color: var(--bg);
  background-color: var(--green);
}
/* RWDRWDRWDRWDRWDRWDRWDRWDRWDRWDRWDRWDRWDRWDRWDRWDRWDRWDRWDRWD */
/* RWDRWDRWDRWDRWDRWDRWDRWDRWDRWDRWDRWDRWDRWDRWDRWDRWDRWDRWDRWD */
/* RWDRWDRWDRWDRWDRWDRWDRWDRWDRWDRWDRWDRWDRWDRWDRWDRWDRWDRWDRWD */

@media screen and (min-width: 450px) {
  .sub-header::after {
    width: 15vw;
    height: 15vw;
    left: 12vw;
  }

  .sub-header::before {
    width: 10vw;
    height: 10vw;
    right: 14vw;
  }

  .sub-header {
    font-size: 2.8em;
  }
}

@media screen and (min-width: 768px) {
  .sub-header::after {
    width: 15vw;
    height: 15vw;
    left: 10vw;
  }

  .sub-header::before {
    width: 13vw;
    height: 13vw;
    right: 12vw;
  }

  .sub-header {
    font-size: 3.2em;
  }
}

@media screen and (min-width: 992px) {
  .sub-header::after {
    width: 13vw;
    height: 13vw;
    left: 10vw;
  }

  .sub-header::before {
    width: 10vw;
    height: 10vw;
    right: 10vw;
  }

  .sub-header {
    font-size: 4em;
  }

  /* 
  big spine
 */
  .spine-big {
    height: auto;
    width: 100%;
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 1.4em;
  }

  .spine-big-circle {
    background-color: var(--green);
    border-radius: 50%;
    width: 40px;
    height: 40px;
  }

  /* spine size */
  .spine-big-circle:nth-child(5),
  .spine-big-circle:nth-child(6),
  .spine-big-circle:nth-child(7) {
    width: 55px;
    height: 55px;
  }

  .spine-big-circle:nth-child(9),
  .spine-big-circle:nth-child(10),
  .spine-big-circle:nth-child(11) {
    width: 70px;
    height: 70px;
  }

  .spine-big-circle:nth-child(13),
  .spine-big-circle:nth-child(14),
  .spine-big-circle:nth-child(15),
  .spine-big-circle:nth-child(17) {
    width: 80px;
    height: 80px;
  }

  .spine-big-circle:nth-child(4n) {
    background-color: var(--blue);
    width: 100px;
    height: 100px;
  }

  .spine-big-circle:nth-child(4),
  .spine-big-circle:nth-child(8) {
    width: 85px;
    height: 85px;
  }

  /* spine position */
  .spine-big-circle:nth-child(1) {
    transform: translateX(100px);
  }

  .spine-big-circle:nth-child(2) {
    transform: translateX(70px);
  }

  .spine-big-circle:nth-child(3) {
    transform: translateX(40px);
  }

  .spine-big-circle:nth-child(4) {
    transform: translateX(10px);
  }

  .spine-big-circle:nth-child(5) {
    transform: translateX(-15px);
  }

  .spine-big-circle:nth-child(6) {
    transform: translateX(-40px);
  }

  .spine-big-circle:nth-child(7) {
    transform: translateX(-55px);
  }

  .spine-big-circle:nth-child(8) {
    transform: translateX(-65px);
  }

  .spine-big-circle:nth-child(9) {
    transform: translateX(-45px);
  }

  .spine-big-circle:nth-child(10) {
    transform: translateX(-15px);
  }

  .spine-big-circle:nth-child(11) {
    transform: translateX(10px);
  }

  .spine-big-circle:nth-child(12) {
    transform: translateX(20px);
  }

  .spine-big-circle:nth-child(13) {
    transform: translateX(5px);
  }

  .spine-big-circle:nth-child(14) {
    transform: translateX(-15px);
  }

  .spine-big-circle:nth-child(15) {
    transform: translateX(-35px);
  }

  .spine-big-circle:nth-child(16) {
    transform: translateX(-60px);
  }

  .spine-big-circle:nth-child(17) {
    transform: translateX(-60px);
  }

  /* 
  spine parts
 */

  main {
    position: relative;
  }

  .spine-circles {
    display: none;
  }

  .spine-part {
    position: absolute;
    top: 0;
    margin-left: 10px;
    margin-right: 10px;
  }

  .spine-part p {
    font-size: 100%;
  }

  .spine-part:nth-child(even) {
    right: 0;
  }

  .spine-part:nth-child(1) {
    top: 0px;
  }

  .spine-part:nth-child(2) {
    top: 360px;
  }

  .spine-part:nth-child(3) {
    top: 740px;
  }

  .spine-part:nth-child(4) {
    top: 1180px;
  }

  .spine-part:nth-child(even) .spine-header h2 {
    text-align: end;
    padding-right: 20px;
  }

  .spine-text {
    border-radius: 0;
    position: relative;
    height: 300px;
    width: 45vw;
    display: flex;
    justify-content: center;
    align-items: center;
    background-color: transparent;
  }

  .spine-text p {
    padding: 100px 25px 100px 0;
  }

  .spine-text::after {
    content: "";
    width: 300px;
    height: 100%;
    right: -150px;
    top: 0;
    background-color: var(--blue);
    position: absolute;
    clip-path: circle(50% at 0 50%);
    z-index: -1;
  }

  .spine-text::before {
    content: "";
    width: calc(100% - 150px);
    height: 100%;
    left: 0;
    top: 0;
    background-color: var(--blue);
    position: absolute;
    z-index: -1;
  }

  .spine-part:nth-child(even) .spine-text::after {
    right: calc(100% - 150px);
    clip-path: circle(50% at 100% 50%);
  }

  .spine-part:nth-child(even) .spine-text::before {
    left: auto;
    right: 0;
  }

  .spine-part:nth-child(even) p {
    padding: 100px 0 100px 25px;
  }
}

@media screen and (min-width: 1200px) {
  .sub-header::after {
    width: 13vw;
    height: 13vw;
    left: 10vw;
  }

  .sub-header::before {
    width: 8vw;
    height: 8vw;
    right: 16vw;
  }

  .sub-header {
    font-size: 4em;
  }

  .spine-part p {
    font-size: 120%;
  }
}