* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: sans-serif;
}

body {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  background: #242837;
}

body .mainForm {
  position: relative;
  width: 380px;
  padding: 25px;
  background-color: #151a26;
  border-radius: 10px;
  display: flex;
  justify-content: center;
  align-items: center;
}

body .mainForm input {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background: none;
  outline: none;
  border: none;
  padding: 15px;
  color: #fff;
  display: flex;
  justify-content: center;
  align-items: center;
}

body .mainForm input::placeholder {
  color: #ccc;
  font-weight: 400;
  font-size: 14px;
}

/* JavaScript */
form.invalid::before {
  content: "";
  position: absolute;
  right: 14px;
  background: url("images/invalid.png") no-repeat center;
  background-size: cover;
  width: 22px;
  height: 22px;
  object-fit: cover;
  transition: 0.4s ease;
}

form.valid::before {
  content: "";
  position: absolute;
  right: 14px;
  background: url("images/valid.png") no-repeat center;
  background-size: cover;
  width: 22px;
  height: 22px;
  object-fit: cover;
  transition: 0.4s ease;
}