flexbox

<div class="row">
			<div class="col-md-2"></div>
			<div class="col-md-8 ">
				<div class="row">
					<article class="col-md-4 bg-primary">
						<h1>Artículo</h1>
					</article>
					<article class="col-md-4 bg-primary">
						<h1>Artículo</h1>
					</article>
					<article class="col-md-4 bg-primary">
						<h1>Artículo</h1>
					</article>
				</div>
			</div>
			<div class=" col-md-2">
			</div>
		</div>

<div class="col-md-8 d-flex justify-content-around">
				<article class="bg-primary">
					<h1>Artículo</h1>
				</article>
				<article class="bg-primary">
					<h1>Artículo</h1>
				</article>
				<article class="bg-primary">
					<h1>Artículo</h1>
				</article>
			</div>

Layout flexbox + media query

 <header>
        <h1>Cabecera</h1>
    </header>
    <div class="slider"></div>
    <main>
        <section>
            <h1>Contenido</h1>
            <p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Hic, esse! Hic magni voluptate quia, ut eligendi
                pariatur deleniti. Numquam, perspiciatis. Eius soluta ipsam qui nisi, ea cum quod atque pariatur?</p>
        </section>
        <section>
            <h1>Contenido</h1>
            <p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Hic, esse! Hic magni voluptate quia, ut eligendi
                pariatur deleniti. Numquam, perspiciatis. Eius soluta ipsam qui nisi, ea cum quod atque pariatur?</p>
        </section>
        <section>
            <h1>Contenido</h1>
            <p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Hic, esse! Hic magni voluptate quia, ut eligendi
                pariatur deleniti. Numquam, perspiciatis. Eius soluta ipsam qui nisi, ea cum quod atque pariatur?</p>
        </section>
        <section>
            <h1>Contenido</h1>
            <p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Hic, esse! Hic magni voluptate quia, ut eligendi
                pariatur deleniti. Numquam, perspiciatis. Eius soluta ipsam qui nisi, ea cum quod atque pariatur?</p>
        </section>
    </main>
    <footer>
        <p>Pie de página</p>
    </footer>

header{
    height:150px;
    background-color: burlywood;
}
.slider{
    width: 100%;
    height: 300px;
    background-image: url('../img/baldosa.jpg');
    background-size: cover;
}
main{
    display: flex;
    flex-wrap: wrap;
}
main section{
    flex:25%;
}
@media (max-width:728px){
    main section{
        flex:50%;
    }
}

@media (max-width:400px){
    .slider{
        height: 100px;
    }
    footer,aside{
        display: none;
    }
    main {
        flex-direction: column;
    }
}

Layout flex responsive

<!DOCTYPE html>
<html>

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <link rel="stylesheet" href="css/layoutflex.css">
</head>

<body>
    <header>
        <h1>Cabecera</h1>
    </header>
    <main>
        <aside>
            <ul>
                <li>aaaa</li>
                <li>aaaa</li>
                <li>aaaa</li>
                <li>aaaa</li>
            </ul>
        </aside>
        <section>
            <h1>Contenido</h1>
            <p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Hic, esse! Hic magni voluptate quia, ut eligendi
                pariatur deleniti. Numquam, perspiciatis. Eius soluta ipsam qui nisi, ea cum quod atque pariatur?</p>
        </section>
    </main>
    <footer>
        <p>Pie de página</p>
    </footer>
</body>

</html>


main{
    display: flex;
}

@media (max-width:728px){
    main{
        flex-direction: column;
    }
}

@media (max-width:400px){
    footer,aside{
        display: none;
    }
}