(wip)appview: add copy button

right now, only the textnode inside the button gets added, without the
<button> around it. can't figure out why. the DataAtom and Type match
what html.Parse gives, per https://go.dev/play/p/eW2o3v2eBbY

appview/pages/markup/markdown.go

···
 	"github.com/yuin/goldmark/text"
 	"github.com/yuin/goldmark/util"
 	htmlparse "golang.org/x/net/html"
+	"golang.org/x/net/html/atom"
 
 	"tangled.sh/tangled.sh/core/appview/pages/repoinfo"
 )
···
 					node.Attr[i] = attr
 				}
 			}
+		}
+
+		if node.Data == "pre" {
+			// TODO only show when :hover or :focus on the pre element
+			button := &htmlparse.Node{
+				Type:     htmlparse.ElementNode,
+				DataAtom: atom.Button,
+				Data:     "button",
+				Attr: []htmlparse.Attribute{
+					{
+						Key: "class",
+						Val: "absolute top-2 right-2 btn",
+					},
+					{
+						Key: "style",
+						// FIXME .#watch-tailwind doesnt seem to catch top-2 and right-2, probably cuz it's not used anywhere inside of templates/ ?
+						Val: "top: 0.5rem; right: 0.5rem;",
+					},
+					{
+						Key: "onclick",
+						Val: `
+							navigator.clipboard.writeText(this.closest('pre').querySelector('code').innerText); 
+							this.innerText = 'Copied!'; 
+							setTimeout(() => { this.innerText = 'Copy' }, 1500);
+						`,
+					},
+					{
+						Key: "onload",
+						Val: "this.removeAttribute('aria-hidden')",
+					},
+					{
+						Key: "aria-hidden",
+						Val: "true",
+					},
+					{
+						Key: "title",
+						Val: "Copy to clipboard",
+					},
+				},
+			}
+
+			// TODO
+			// if copyIcon, err := icons.IconNode("copy", "h-4", "w-4"); err != nil {
+			// 	button.AppendChild(copyIcon)
+			// } else {
+			button.AppendChild(&htmlparse.Node{
+				Type: htmlparse.TextNode,
+				Data: "Copy",
+			})
+
+			var classWasSetOnNode bool
+			for i, attr := range node.Attr {
+				if attr.Key == "class" {
+					node.Attr[i].Val += " relative"
+					classWasSetOnNode = true
+					break
+				}
+			}
+
+			if !classWasSetOnNode {
+				node.Attr = append(node.Attr, htmlparse.Attribute{
+					Key: "class",
+					Val: "relative",
+				})
+			}
+
+			node.AppendChild(button)
 		}
 
 		for n := node.FirstChild; n != nil; n = n.NextSibling {