<picture>
    <source srcset="/img/header/1.webp" media="(min-width: 766px)">
    <source srcset="/img/header/2.webp" media="(max-width: 766px)">
    <img src="/img/header/1.jpg" alt="">
</picture><picture>
    <source srcset="/img/header/1.webp" media="(min-width: 766px)">
    <source srcset="/img/header/2.webp" media="(max-width: 766px)">
    <img src="/img/header/1.jpg" class="desktop" alt="">
    <img src="/img/header/2.jpg" class="mobile" alt="">
</picture>.mobile{ display:none; }
@media all and (max-width:766px){
   .mobile{ display:block; }
   .desktop{ display:none; }
}