Gradient between image tag and gray background

Question

I’m creating a project and I wanted to make a gradient between the background image and the dark gray background that’s just below, someone knows how to do that?

My current code is:

@import url('https://fonts.googleapis.com/css?family=Manjari&display=swap');
*{
margin: 0;
padding: 0;
outline: 0;
box-sizing: border-box;
}
html, body, #root, .render{
height: 100%;
}
body{
    background: #111;
    font-family: 'Manjari', sans-serif;
}
.mainBanner{
    background: url('https://i.ibb.co/7XY9yyb/fundo.jpg');
    height: 100%;
    width: 100%;
}
.wall{
    background: rgba(0, 0, 0, 0.5);
    height: 100%;
    overflow: auto;
    width: 100%;
}
.topContainer{
    margin-top: 15px;
}
.topContainer h1{
    font-size: 35px;
    text-align: center;
    color: #e50914;
}
.wellcomemsg{
    text-align: center;
    margin-top: 280px;
    font-size: 80px;
    text-shadow: 1px 2px 3px rgba(255,255,255,0.6);
    color: #FFF;
}
.btns button{
    margin: 0 auto;
    padding: 15px 20px;
    margin-top: 5px;
    cursor: pointer;
    border-radius: 3px;
    margin-left: 10px;
    border: 1px solid #e50914;
    background: #e50914;
    color: #FFF;
    font-size: 22px;
}
.multi{
    position: relative;
}
.multi p{
    color: #FFF;
    font-size: 40px;
    word-wrap: break-word;
    float: right;
    margin-right: 70px;
    margin-top: 12%;
}
.multi img{
    margin-bottom: 5%;
    opacity: 0.8;
    margin-left: 60px;
    width: 30%;
    margin-top: 4%;
    cursor: pointer;
}
.multi img:hover{
    opacity: 1;
}
hr{
    border-color: #ccc; 
    width: 90%;
    margin: 0 auto;
}
@media only screen and (max-width: 600px) {
    .wellcomemsg{
        font-size: 50px;
        margin-top: 50px;
    }
    .btns button{
        margin-top: 20px;
        font-size: 20px;
    }
    .multi img{
        margin-top: 30px;
        width: 90%;
        margin-left: 5%;
    }
    .multi p{
        width: 100%;
        margin-top: 8%;
        margin-right: 0;
        text-align: center;
        font-size: 20px;
    }
}

        <div class="render">
        <div class="mainBanner">
            <div class="wall">
                <div class="topContainer">
                    <h1>IMM | YouWatch</h1>
                </div>
                <div class="wellcomemsg">
                    <p>Bem-vindo a YouWatch</p>
                    <p>Experimenta Gratis durante</p>
                    <p>1 Mês</p>
                    <div class="btns">
                        <button>Criar uma conta</button>
                        <button>Iniciar Sessão</button>
                    </div>
                </div>
            </div>
        </div>
        <div class="multi">
        <img src="https://i.ibb.co/q9s3R9v/multi.png" alt="Multi Plataformas" title="Multi Plataformas"/>
        <p>Veja os seus filmes e series favoritos onde e quando quiser!</p>
        </div>
        <hr />
        <p>T</p>
        </div>