modal.css

:root {
    /* Variables */
    --color-primary: #ff5544;
    --font-default: 'Roboto', Arial, Helvetica, sans-serif;
    --font-slab: 'Roboto Slab', var(--font-default);

    font-family: var(--font-default);
    font-size: 18px;
}

body {
    margin: 0;
    display: flex;
    flex-direction: column;
}

nav {
    color: #444;
    background-color: white;
    font-family: var(--font-slab);
    text-transform: uppercase;
    font-size: 90%;
    padding: 0 10vw;
    display: flex;
    box-shadow: 0 0.1rem 0.1rem rgba(0, 0, 0, 0.5);
    z-index: 1;
}

nav a {
    color: inherit;
    font-family: inherit;
    text-decoration: none;
    padding: 1rem 2rem;
    display: block;
    transition: all 0.05s linear;
}

nav a span {
    position: relative;
}

nav a span::after {
    content: '';
    display: block;
    width: 0;
    height: 0.1rem;
    background-color: var(--color-primary);
    position: absolute;
    transition: all 0.15s ease-in-out;
}

nav a:hover span::after {
    width: 100%;
}

nav a:hover {
    background-color: rgba(0, 0, 0, 0.05);
    color: var(--color-primary);
}

main {
    font-size: 140%;
    background-color: var(--color-primary);
    color: white;
    padding: 10vw;
    display: flex;
    flex-direction: column;
    background-image: url('background.png');
    align-items: flex-start;
}

main button {
    color: var(--color-primary);
    font-family: var(--font-slab);
    background-color: white;
    border: 0;
    padding: 0.75rem 2.5rem;
    font-size: inherit;
    border-radius: 5rem;
    border: 0.1em solid white;
    cursor: pointer;
    transition: 0.075s all ease-out;
}

main button:hover {
    background-color: transparent;
    color: white;
}

/*
    Modal styles
*/

.modal.open {
    display: flex;
}

.modal {
    display: none;
    position: fixed;
    justify-content: center;
    align-items: flex-start;
    background-color: rgba(0, 0, 0, 0.6);
    top: 0;
    left: 0;
    bottom: 0;
    right: 0;
    z-index: 2;
    padding: 10vh 0;
}

.modal .container {
    background-color: white;
    border-radius: 0.25rem;
    width: 50vw;
    padding: 2rem;
    position: relative;
}

.modal .close-button {
    font-size: 150%;
    background-color: transparent;
    border: 0;
    cursor: pointer;
    position: absolute;
    top: 0.3rem;
    right: 0.5rem;
}