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

body {
  width: 100vw;
  height: 100vh;
  background: #34495e;
}

main {
  position: absolute;
  left: 50%;
  top: 50%;
  transform: translate(-50%, -50%);
  width: 300px;
  height: 300px;
  border: solid 5px silver;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
}

.field {
  position: relative;
  overflow: hidden;
  margin-bottom: 20px;
}

.field::before {
  content: '';
  position: absolute;
  left: 0;
  height: 2px;
  bottom: 0;
  width: 100%;
  background: linear-gradient(to right, white, #1abc9c, #f1c40f, #e74c3c, white);
  transform: translateX(-100%);
  transition: 2s;
}

.field:hover::before {
  transform: translateX(100%);
}

.field input {
  border: none;
  outline: none;
  background: #ecf0f1;
  padding: 10px;
}