[MUI] 텍스트필드 플레이스홀더 스타일링

 /* placeholder 스타일 */
  & .MuiInputBase-input {
    &::placeholder {
      font-size: 15px;
      font-weight: 500;
      letter-spacing: 0%;
      color: #cccccc !important;
      opacity: 1;
    }
    &::-webkit-input-placeholder {
      font-size: 15px;
      font-weight: 500;
      letter-spacing: 0%;
      color: #cccccc !important;
      opacity: 1;
    }
    &::-moz-placeholder {
      font-size: 15px;
      font-weight: 500;
      letter-spacing: 0%;
      color: #cccccc !important;
      opacity: 1;
    }
    &:-ms-input-placeholder {
      font-size: 15px;
      font-weight: 500;
      letter-spacing: 0%;
      color: #cccccc !important;
      opacity: 1;
    }
  }