When choosing a picture in a block, I need to switch the main picture
Where do I start?
You can create a JavaScript function which could do it,
function SlideShow(n) {
var i;
var slides = document.getElementsByClassName("");
var circles = document.getElementsByClassName("");
if (n > slides.length) {
slidePosition = 1
}
if (n < 1) {
slidePosition = slides.length
}
for (i = 0; i < slides.length; i++) {
slides[i].style.display = "none";
}
for (i = 0; i < circles.length; i++) {
circles[i].className = circles[i].className.replace(" enable", "");
}
slides[slidePosition-1].style.display = "block";
circles[slidePosition-1].className += " enable";
}
And of course CSS!
Or you can use onclick methods to make another way of functionality.