copy-code-button.css

<style>
  .codeblock--name {
    width: fit-content;
    /* margin: 1rem 0 0; */
    font-size: 0.9rem;
    color: white;
    /* background-color: #272822; */
    background-color: #4f4f4f;
    padding: 0.3rem 0.8rem !important;
    /* font-weight: 400; */
    border-radius: 0.3rem;
    /* margin-top: -20px !important; */
    margin-bottom: -0.3rem;
  }
  .codeblock--contet {
    margin-top: 0;
  }
  pre {
    margin-top: 0rem !important;
  }
  .highlight-wrapper {
  display: block;
  }

  .highlight {
    position: relative;
    z-index: 0;
    padding: 0;
    margin: 0;
    border-radius: 4px;
  }

  .highlight > .chroma {
    color: #d0d0d0;
    background-color: #212121;
    position: static;
    z-index: 1;
    border-radius: 4px;
    padding: 10px;
  }

  .chroma .lntd:first-child {
    padding: 7px 7px 7px 10px;
    margin: 0;
  }

  .chroma .lntd:last-child {
    padding: 7px 10px 7px 7px;
    margin: 0;
  }

  .copy-code-button {
    position: absolute;
    z-index: 2;
    right: 0;
    top: 0;
    /* font-size: 1.5em; */
    font-weight: 700;
    line-height: 14px;
    letter-spacing: 0.5px;
    height: 2rem;
    width: 65px;
    color: #232326;
    background-color: #7f7f7f;
    border: 1.25px solid #232326;
    border-top-left-radius: 0;
    border-top-right-radius: 3px;
    border-bottom-right-radius: 0;
    border-bottom-left-radius: 4px;
    white-space: nowrap;
    padding: 4px 4px 5px 4px;
    margin: 0 0 0 1px;
    cursor: pointer;
    opacity: 0.6;
  }

  .copy-code-button:hover,
  .copy-code-button:focus,
  .copy-code-button:active,
  .copy-code-button:active:hover {
    color: #222225;
    background-color: #b3b3b3;
    opacity: 0.8;
  }

  .copyable-text-area {
    position: absolute;
    height: 0;
    z-index: -1;
    opacity: .01;
  }

</style>

copy-code-button.html

<script>
const copyIcon = '<i class="fa-solid fa-clone fa-lg"></i>';
function createCopyButton(highlightDiv) {
    const button = document.createElement("button");
    button.innerHTML = copyIcon;
    button.className = "copy-code-button";
    button.type = "button";
    button.addEventListener("click", () => copyCodeToClipboard(button, highlightDiv));
    addCopyButtonToDom(button, highlightDiv);
}

async function copyCodeToClipboard(button, highlightDiv) {
    const codeElement = highlightDiv.querySelector("code");
    let codeToCopy = "";
    if (codeElement) {
        codeToCopy = codeElement.innerText;
    } else {
        const codeLines = highlightDiv.querySelectorAll("td");
        codeLines.forEach((codeLine, index) => {
            if ( (index+1) % 2 === 0) {
                codeToCopy += codeLine.innerText + "\n";
            }
        });
    }
    try {
        result = await navigator.permissions.query({ name: "clipboard-write" });
        if (result.state == "granted" || result.state == "prompt") {
        await navigator.clipboard.writeText(codeToCopy);
        } else {
        copyCodeBlockExecCommand(codeToCopy, highlightDiv);
        }
    } catch (_) {
        copyCodeBlockExecCommand(codeToCopy, highlightDiv);
    }
    finally {
        codeWasCopied(button);
    }
}

function copyCodeBlockExecCommand(codeToCopy, highlightDiv) {
    const textArea = document.createElement("textArea");
    textArea.contentEditable = 'true'
    textArea.readOnly = 'false'
    textArea.className = "copyable-text-area";
    textArea.value = codeToCopy;
    highlightDiv.insertBefore(textArea, highlightDiv.firstChild);
    const range = document.createRange()
    range.selectNodeContents(textArea)
    const sel = window.getSelection()
    sel.removeAllRanges()
    sel.addRange(range)
    textArea.setSelectionRange(0, 999999)
    document.execCommand("copy");
    highlightDiv.removeChild(textArea);
}

function codeWasCopied(button) {
    button.blur();
    button.innerText = "Copied";
    setTimeout(function() {
        button.innerHTML = copyIcon;
    }, 2000);
}

function addCopyButtonToDom(button, highlightDiv) {
    highlightDiv.insertBefore(button, highlightDiv.firstChild);
    const wrapper = document.createElement("div");
    wrapper.className = "highlight-wrapper";
    highlightDiv.parentNode.insertBefore(wrapper, highlightDiv);
    wrapper.appendChild(highlightDiv);
}

document.querySelectorAll(".highlight").forEach(highlightDiv => createCopyButton(highlightDiv));
</script>