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;
    }
}

Media queries para dispositivos

En w3school:

https://www.w3schools.com/css/css_rwd_mediaqueries.asp

Ejemplos:

https://www.w3schools.com/css/css3_mediaqueries_ex.asp

Tutorial bastante completo:

https://www.adictosaltrabajo.com/2012/10/11/css3-media-queries/

En css trick:

https://css-tricks.com/a-complete-guide-to-css-media-queries/

Lista de resoluciones para todos los dispositivos:

Media Queries for Standard Devices

Las más comunes:

https://responsivedesign.is/develop/browser-feature-support/media-queries-for-common-device-breakpoints/

Un artículo muy bueno sobre uso de media query.

https://www.toptal.com/designers/responsive/introduction-to-responsive-web-design-pseudo-elements-media-queries

 

Qué es el diseño responsive:

https://i.workana.com/glosario/que-es-el-diseno-responsive/

Ejemplos responsive:

https://web.dev/responsive-web-design-basics/

9 principios del diseño responsive:

https://blog.froont.com/9-basic-principles-of-responsive-web-design/