styles.css

* {
    box-sizing: border-box;
}

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    font-size: 1rem;
    margin: 0;
    padding: 0;
    display: flex;
    gap: 2rem;
    min-height: 100vh;
}

a {
    color: #4042e3;
    text-decoration: none;
}

a:hover {
    text-decoration: underline;
}

a:visited {
    color: #12137b;
}

button {
    font-size: inherit;
    font-family: inherit;
    color: #fff;
    background-color: #4042e3;
    padding: 1rem;
    border-radius: 1rem;
    border-width: 0;
    min-width: 30ch;
    box-shadow: 0px 1px 3px #313131;
}

button:hover {
    cursor: pointer;
    opacity: 0.8;
}

button:active {
    outline: none;
    box-shadow: inset 0px 1px 3px #12137b;
}

.left-side {
    display: flex;
    flex-direction: column;
    justify-content: flex-end;
    align-items: center;

    padding: 0.5rem 1rem;
    min-width: 28rem;
    background: url('images/background.jpg') center no-repeat;
    background-size: 100%;
}

.right-side {
    display: flex;
    flex-direction: column;
    justify-content: center;
    gap: 2rem;
}

.right-side .text {
    margin-right: 1rem;
}

.form-container {
    background-color: #ececec;
}

.signup-form {
    display: flex;
    flex-wrap: wrap;
    gap: 1rem;

    padding: 1rem;
    box-shadow: 0px 1px 3px #313131;
    border-radius: 5px 0px 0px 5px;
}

.form-element {
    display: flex;
    flex-direction: column;
}

.form-element p {
    margin: 0;
    color: #e21d1f;
    display: none;
}

label {
    font-size: 0.7rem;
}

input {
    min-width: 30vw;
}

input:focus {
    outline:none;
    border: 3px solid #4042e3;
}

input:not(:focus):invalid {
    color: #e21d1f;
    border: 2px solid #e21d1f;
}

input:not(:focus):invalid + p {
    display: initial;
}