css | CSS: dispondo elementos com Flexbox e Grid | Alura

Meu css dessa aula não está funfando, alguem pode me ajudar ?

html

<!DOCTYPE html>
    <main class="principal">
        <h2 class="titulo-pagina">Inicio</h2>
        <article class="cartao">
            <img src="assets/img/banner-mobile_1.png" alt="Banner do cartao" class="cartao__imagem">
            <div class="cartao__conteudo">
                <p class="cartao__destaque">Video em Destaque</p>
                <h3 class="cartao__titulo">HZC - Titulo</h3>
                <p class="cartao__perfil">Bruno Lopez</p>
                <p class="cartao__info cartao__info--tempo">33 minutos</p>
                <p class="cartao__info cartao__info--visualizacao">33 visualizações</p>
                <button class="cartao__botao cartao__botao--play cartao__botao--destaque">Assistir agora</button>
            </div>

        </article>
    </main>

    <script src="index.js"></script>
</body>
</html>

CSS

@font-face {
    font-family: 'icones';
    src: url(../font/icones.ttf);
}
body {
    background-color: #1D232A;
    font-family: 'open Sans', 'icones', sans-serif;
    color: #ffffff;
}
.cabecalho {
    display: flex;
    justify-content: space-between;
    align-items: center;
    background-color: #15191C;
    padding: 8px 16px;
    box-shadow: 0px 4px 4px rgba(0, 0, 0, 0.16);
}

.cabecalho__menu i::before {
    content: "\e904";
    font-size: 24px;
}
.cabecalho__notificacao i::before {
    content: "\e906";
    font-size: 24px;
}

.cabecalho__logo {
    width: 40px;
}

.menu-lateral {
    display: flex;
    flex-direction: column;
    background-color: #15191C;
    width: 75vw;
    height: 100vh;
    position: absolute;
    left: -100vw;
    transition: .25s;
}

.menu-lateral--ativo {
    left: 0;
    transition: .25s;
}

.menu-lateral__logo {
    width: 118px;
    align-self: center;
    padding: 16px;
}

.menu-lateral__link {
    height: 64px;
    color: #95999C;
    padding-left: 64px;
    display: flex;
    align-items: center;
}

.menu-lateral__link--ativo {
    color: #ffffff;
    padding-left: 56px;
    border-left: 9px solid #ffffff;
}

.menu-lateral__link::before {
    content: "";
    width: 24px;
    height: 24px;
    font-size: 24px;
    position: absolute;
    left: 24px;
}

.menu-lateral__link--inicio::before {
    content: "\e902";
}

.menu-lateral__link--videos::before {
    content: "\e90e";
}
.menu-lateral__link--picos::before {
    content: "\e909";
}
.menu-lateral__link--integrantes::before {
    content: "\e903";
}
.menu-lateral__link--camisas::before {
    content: "\e900";
}
.menu-lateral__link--pinturas::before {
    content: "\e90a";
}

.principal {
    padding: 24px 16px;
}

.titulo-pagina {
    font-size: 1.5rem;
    font-weight: 700;
}

.cartao {
    width: 100%;
    border-radius: 15px;
    overflow: hidden;
    background-color: #2C343A;
}

.cartao__conteudo {
    padding: 16px;
}

.cartao__titulo {
    font-size: 1.2rem;
    font-weight: 700;
}

.cartao__perfil {
    color: #95999C;
    font-size: 0.9rem;
}

.cartao__info {
    display: flex;
    align-items: center;
    color: #95999C;
}

.cartao__info--tempo {
    content: "\e90c";
    margin-right: 8px;
}

.cartao__info--visualizacao {
    content: "\e90f";
    margin-right: 8px;
}

.cartao__botao {
    display: flex;
    justify-content: center;
    align-items: center;
    background-color: #2C343A;
    width: 48px;
    height: 48px;
    border-radius: 10px;
    font-size: 0.9rem;
}

.cartao__botao--play::before {
    content: \e90b;
    font-size: 24px;
}

.cartao__botao--destaque {
    width: 100%;
}

.cartao__botao--destaque::before {
    margin-right: 8px;
}