HTMLify

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

:root {
    --input: #ffffff;
    --primary: #255ff4;
    --dur: 1s;
}

body,
input {
    color: #e3e4e8;
    font: 1em/1.5 Hind, sans-serif;
}

body {
    background: #17181c;
    display: flex;
    height: 100vh;
}

:is(form, input, .caret) {
    margin: auto;
}

form {
    position: relative;
    width: 100%;
    max-width: 17em;
}

input,
.caret {
    display: block;
    transition: all calc(var(--dur) * 0.5) linear;
}

input {
    background: transparent;
    border-radius: 50%;
    box-shadow: 0 0 0 0.25em inset;
    caret-color: var(--primary);
    width: 2em;
    height: 2em;
    -webkit-appearance: none;
    -moz-appearance: none;
    appearance: none;
}

input:focus,
input:valid {
    background: var(--input);
    border-radius: 0.25em;
    box-shadow: none;
    padding: 0.75em 1em;
    transition-duration: calc(var(--dur) * 0.25);
    transition-delay: calc(var(--dur) * 0.25);
    width: 100%;
    height: 3em;
}

input:focus {
    animation: showCaret var(--dur) steps(1);
    outline: transparent;
}

input:focus+.caret,
input:valid+.caret {
    animation: handleToCaret var(--dur) linear;
    background: transparent;
    width: 1px;
    height: 1.5em;
    transform: translate(0, -1em) rotate(-180deg) translate(7.5em, -0.25em);
}

input::-webkit-search-decoration {
    -webkit-appearance: none;
}

label {
    color: #e3e4e8;
    overflow: hidden;
    position: absolute;
    width: 0;
    height: 0;
}

.caret {
    background: currentColor;
    border-radius: 0 0 0.125em 0.125em;
    margin-bottom: -0.6em;
    width: 0.25em;
    height: 1em;
    transform: translate(0, -1em) rotate(-45deg) translate(0, 0.875em);
    transform-origin: 50% 0;
}

/* Animations */
@keyframes showCaret {
    from {
        caret-color: transparent;
    }

    to {
        caret-color: var(--primary);
    }
}

@keyframes handleToCaret {
    from {
        background: currentColor;
        width: 0.25em;
        height: 1em;
        transform: translate(0, -1em) rotate(-45deg) translate(0, 0.875em);
    }

    25% {
        background: currentColor;
        width: 0.25em;
        height: 1em;
        transform: translate(0, -1em) rotate(-180deg) translate(0, 0.875em);
    }

    50%,
    62.5% {
        background: var(--primary);
        width: 1px;
        height: 1.5em;
        transform: translate(0, -1em) rotate(-180deg) translate(7.5em, 2.5em);
    }

    75%,
    99% {
        background: var(--primary);
        width: 1px;
        height: 1.5em;
        transform: translate(0, -1em) rotate(-180deg) translate(7.5em, -0.25em);
    }

    87.5% {
        background: var(--primary);
        width: 1px;
        height: 1.5em;
        transform: translate(0, -1em) rotate(-180deg) translate(7.5em, 0.125em);
    }

    to {
        background: transparent;
        width: 1px;
        height: 1.5em;
        transform: translate(0, -1em) rotate(-180deg) translate(7.5em, -0.25em);
    }
}