Expanding Flex Cards/style.css
@import url('https://fonts.googleapis.com/css2?family=Poppins:wght@200;300;400;600&display=swap');

body {
  background: linear-gradient(
    45deg,
    rgba(18, 71, 96, 0.88),
    rgba(194, 30, 30, 0.8),
    rgba(97, 51, 193, 0.8),
    rgba(70, 11, 7, 0.88)
  );

  display: flex;
  flex-direction: row;
  justify-content: center;
  align-items: center;
  overflow: hidden;
  height: 100vh;
  font-family: "poppins", sans-serif;
}

body .options {
  display: flex;
  flex-direction: row;
  align-items: stretch;
  overflow: hidden;
  min-width: 600px;
  max-width: 900px;
  width: calc(100% - 100px);
  height: 400px;
}

body .options .option {
  position: relative;
  overflow: hidden;
  min-width: 60px;
  margin: 10px;
  background: var(--optionBackground, var(--defaultBackground, #E6E9ED));
  background-size: auto 120%;
  background-position: center;
  cursor: pointer;
  transition: 0.5s cubic-bezier(0.05, 0.61, 0.41, 0.95);
}

body .options .option.active {
  flex-grow: 10000;
  transform: scale(1);
  max-width: 600px;
  margin: 0px;
  border-radius: 40px;
  background-size: auto 100%;
  border: 5px solid #fff;
}

body .options .option:not(.active) {
  flex-grow: 1;
  border-radius: 30px;
}

body .options .option .label {
  display: flex;
  position: absolute;
  right: 0px;
  height: 40px;
  transition: 0.5s cubic-bezier(0.05, 0.61, 0.41, 0.95);
}

body .options .option:not(.active) .label {
  bottom: 10px;
  left: 10px;
}

body .options .option.active .label{
  bottom: 20px;
  left: 20px;
}

body .options .option .label .icon{
  display: flex;
  flex-direction: row;
  justify-content: center;
  align-items: center;
  min-width: 40px;
  max-width: 40px;
  height: 40px;
  border-radius: 100%;
  background: #FFF;
  color: var(--defaultBackground);
}

body .options .option .label .info{
  display: flex;
  flex-direction: column;
  justify-content: center;
  margin-left: 10px;
  color: #fff;
  white-space: pre;
}

body .options .option .label .info > div{
  position: relative;
  transition: 0.5s cubic-bezier(0.05, 0.61, 0.41, 0.95), opacity 0.5s ease-out;
}

body .options .option .label .info .main {
  font-weight: normal;
  font-size: 1rem;
  text-transform: uppercase;
}

body .options .option .label .info .sub {
  transition-delay: 0.1s;
  font-size: 0.8rem;
  text-transform: uppercase;
}

body .options .option:nth-child(1) {
  --defaultBackground:#ED5565;
}
body .options .option:nth-child(2) {
  --defaultBackground:#FC6E51;
}
body .options .option:nth-child(3) {
  --defaultBackground:#FFCE54;
}
body .options .option:nth-child(4) {
  --defaultBackground:#2ECC71;
}
body .options .option:nth-child(5) {
  --defaultBackground:#5D9CEC;
}
body .options .option:nth-child(6) {
  --defaultBackground:#AC92EC;
}

@media screen and (max-width: 718px) {
  body .options {
    min-width: 520px;
  }
  body .options .option:nth-child(5) {
    display: none;
  }
}

@media screen and (max-width: 638px) {
  body .options {
    min-width: 440px;
  }
  body .options .option:nth-child(4) {
    display: none;
  }
}

@media screen and (max-width: 558px) {
  body .options {
    min-width: 360px;
  }
  body .options .option:nth-child(3) {
    display: none;
  }
}

/* Coded With ❤ By Priyanshu Mohanty */