Cart: Add sneak-peek preview (#3259)

src/pretix/static/pretixpresale/js/ui/main.js

@@ -288,6 +288,30 @@ $(function () {
 
     $("#ajaxerr").on("click", ".ajaxerr-close", ajaxErrDialog.hide);
 
+    $('details.sneak-peek:not([open])').each(function() {
+        this.open = true;
+        var $elements = $("> :not(summary)", this).show().filter(':not(.sneak-peek-trigger)').attr('aria-hidden', 'true');
+
+        var container = this;
+        var trigger = $('summary, .sneak-peek-trigger button', container);
+        function onclick(e) {
+            e.preventDefault();
+
+            container.addEventListener('transitionend', function() {
+                $(container).removeClass('sneak-peek');
+                container.style.removeProperty('height');
+            }, {once: true});
+            container.style.height = container.scrollHeight + 'px';
+            $('.sneak-peek-trigger', container).fadeOut(function() {
+                $(this).remove();
+            });
+            $elements.removeAttr('aria-hidden');
+
+            trigger.off('click', onclick);
+        }
+        trigger.on('click', onclick);
+    });
+
     // Copy answers
     $(".js-copy-answers").click(function (e) {
         e.preventDefault();

src/pretix/static/pretixpresale/scss/main.scss

@@ -398,6 +398,27 @@ details.details-open .panel-heading .collapse-indicator,
     transform: rotate(180deg);
 }
 
+details.sneak-peek {
+    position: relative;
+    height: 11em;
+    overflow: hidden;
+    transition: height .5s;
+}
+.sneak-peek-trigger {
+    display: grid;
+    justify-content: center;
+    align-content: center;
+    width: 100%;
+    height: 4.5em;
+    margin: 0;
+    padding: 15px;
+    background: linear-gradient(0deg, rgba(248,248,248,.9) 44%, rgba(248,248,248,0) 100%);
+    position: absolute;
+    bottom: 0;
+    left: 0;
+    z-index: 10;
+}
+
 form.download-btn-form {
     display: inline;
 }