screen.css

@import url("https://fonts.googleapis.com/css2?family=Roboto:wght@400;700&display=swap");

/* start reset */

html, body, div, p, h1, h2, h3, h4, h5, h6,
ul, ol, li, dl, dt, dd, form, fieldset, caption, legend,
table, tr, td, th, address, blockquote, img {
    margin: 0;
    padding: 0;
}

img, fieldset {
    border: none;
}

blockquote, q {
    quotes: none;
}

html {
    box-sizing: border-box;
}

*, *::before, *::after {
    box-sizing: inherit;
}

button, label, summary {
    cursor: pointer;
}

body, button, input, table, textarea, select {
    font-size: 1rem;
    line-height: 1.5;
    font-family: inherit;
}

button {
    background: none;
    border: none;
    cursor: pointer;
}

ul {
    list-style: none;
}

a {
    text-decoration: none;
}

/* end reset */

:root {
    --tomato: hsl(4, 100%, 67%);
    --tomato-bg: hsla(4, 100%, 67%, 0.2);
    --dark-slate-grey: hsl(234, 29%, 20%);
    --dark-slate-grey-hov: hsla(234, 29%, 20%, 0.9);
    --charcoal-grey: hsl(235, 18%, 26%);
    --grey: hsl(231, 7%, 60%);
    --white: hsl(0, 0%, 100%);
}

html {
    height: 100%;
}

body {
    min-height: 100%;
    font: 400 1em/1.5 Roboto, sans-serif;
    display: flex;
    align-items: center;
    justify-content: start;
    flex-direction: column;
}

article {
    background-image: url(assets/images/illustration-sign-up-mobile.svg);
    background-repeat: no-repeat;
    background-position: center top;
    background-color: #fff;
    max-width: 26em;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

section {
    height: 100%;
    padding: 20.3em 1.75em 1.75em 1.75em;
}

h1 {
    font-size: 2.5em;
    line-height: 1;
    margin: 0 0 0.6em;
    color: var(--dark-slate-grey);
}

p {
    margin: 0.5em 0 1em;
    font-weight: 300;
    color: var(--dark-slate-grey);
}

ul {
    display: flex;
    row-gap: .25em;
    flex-direction: column;
    margin: 0 0 2em;
    color: var(--dark-slate-grey);
}

li {
    line-height: 24px;
    display: flex;
    column-gap: .5em;
    margin: 0.25em 0;
    position: relative;
    padding-left: calc(24px + 0.625em);
}

li::before {
    content: '';
    position: absolute;
    left: 0;
    top: 0;
    width: 24px;
    height: 24px;
    background: url(assets/images/icon-list.svg) 0 0 no-repeat;
}

label, .fieldHint {
    color: var(--dark-slate-grey);
    font: 700 0.75em/1.5 Roboto, sans-serif;
    display: block;
    padding: 0 0 .5em;
    flex-basis: 50%;
    flex-grow: 1;
}

.fieldHint {
    color: var(--tomato);
    margin-left: auto;
    text-align: right;
    display: none;
}

form.invalid .fieldHint {
    display: block;
}

form {
    width: 100%;
    display: flex;
    flex-direction: row;
    flex-wrap: wrap;
}

input, .button, button {
    display: block;
    border: 1px solid var(--grey);
    width: 100%;
    padding: 1em;
    border-radius: 0.5em;
    margin: 0 0 1.5em;
    flex-basis: 100%;
    white-space: nowrap;
}

button {
    padding: 1em 0 1em;
}

form.invalid input {
    background-color: var(--tomato-bg);
    border: 0.075em solid var(--tomato);
    color: var(--tomato);
}

form.invalid input::placeholder {
    color: var(--tomato);
}

form.invalid input:focus {
    outline-color: var(--tomato);
}

button,
.button {
    text-align: center;
    background: var(--dark-slate-grey);
    border: 0;
    color: #fff;
    font-weight: 700;
    transition: background .3s ease;
    cursor: pointer;
}

button:hover,
.button:hover {
    background: var(--dark-slate-grey-hov);
}

article.success {
    background-image: url(assets/images/icon-success.svg);
    background-position: left 2em top 9.25em;
    padding-top: 14em;
}

article.success section {
    display: flex;
    flex-direction: column;
    padding-top: 2em;
    flex-grow: 1;
}

article.success .button {
    margin-top: auto;
    flex-basis: auto;
}

footer {
    opacity: 0.5;
    gap: 0.25rem;
    text-align: right;
    display: flex;
    align-items: center;
    flex-direction: column;
    margin: auto 0 1.75em;
    font-size: 0.875em;
    font-weight: 700;
    color: var(--dark-slate-grey);
}

footer a {
    color: var(--dark-slate-grey);
    opacity: 0.45;
}

@media (min-width: 49.5em) {
    html {
        height: 100%;
    }

    body {
        min-height: 100%;
        display: flex;
        align-items: center;
        justify-content: center;
        background: var(--dark-slate-grey);
    }

    article {
        display: flex;
        max-width: 100%;
        flex-direction: row;
        justify-content: space-around;
        align-items: start;
        width: 60em;
        height: 40em;
        background-image: url(assets/images/illustration-sign-up-desktop.svg);
        background-position: right 1.5em top 1.5em;
        border-radius: 1.5em;
        margin: 0 1em 0;
        min-height: auto;
        flex-wrap: wrap;
    }

    section {
        flex-basis: 40%;
        padding: 5.5em 0 0 0;
    }

    section + div {
        height: 100%;
        flex-basis: 400px;
    }

    article.success {
        width: 32em;
        height: 32em;
        padding: 0;
        background-position: top 3em left 3em;
    }

    article.success section {
        padding: 10em 3em 2em;
    }

    article.success h1 {
        white-space: normal;
        line-height: 1;
    }

    h1 {
        font: 700 3.5em/1.5 Roboto, sans-serif;
        white-space: nowrap;
        margin: 0;
    }

    footer {
        height: 2.5rem;
        flex-direction: row;
        justify-content: flex-end;
        gap: 0.625em;
        margin: 0;
        padding: 0 0.5em;
        line-height: 2;
        color: #AAA;
        flex-basis: 100%;
    }

    footer a {
        color: #AAA;
    }
}