HTMLify

body {
    text-align: center;
    display: flex;
    align-items: center;
    justify-content: center;
    height: 100vh;
    background-color: #151515;
}

input {
    font-family: sans-serif;
    line-height: 1.5;
    font-size: 1.5rem;
    color: #fff;
    background-color: #151515;
    min-width: 12em;
}

::placeholder {
    color: #fff;
}

.input_wrapper {
    position: relative;
    background: linear-gradient(21deg, #10abff, #1beabd);
    padding: 2px;
    display: inline-block;
}

.input_wrapper *:not(span) {
    position: relative;
    display: inherit;
    margin: 0;
    border: none;
    outline: none;
    padding: 0.7em;
    z-index: 1;
}

.input_wrapper *:not(span):focus+span {
    opacity: 1;
    transform: scale(1);
}

.input_wrapper span {
    transform: scale(0.993, 0.94);
    transition: transform 0.5s, opacity 0.25s;
    opacity: 0;
    position: absolute;
    z-index: 0;
    margin: 4px;
    inset: 0;
    pointer-events: none;
    box-shadow: inset 3px -3px 30px #1beabd, -3px 3px 30px #10abff;
}