<div class="vtabs-wrapper blush-cards">
  <div class="vtabs-cont">
    <div class="vtab-buttons">
      <button class="vtab-btn">Вкладка 1</button>
      <button class="vtab-btn">Вкладка 2</button>
      <button class="vtab-btn">Вкладка 3</button>
      <button class="vtab-btn">Вкладка 4</button>
    </div>
    <div class="vtab-content">Содержимое 1</div>
    <div class="vtab-content">Содержимое 2</div>
    <div class="vtab-content">Содержимое 3</div>
    <div class="vtab-content">Содержимое4</div>
  </div>
</div>

Код:
<!-- вкладки для ЛС без ID by Vandra  -->
<script>
function initTabs(modal) {
    modal.querySelectorAll(".vtabs-cont").forEach(tabContainer => {
        const buttons = tabContainer.querySelectorAll(".vtab-btn");
        const tabs = tabContainer.querySelectorAll(".vtab-content");

        if (!buttons.length || !tabs.length) return;

        if (tabContainer.dataset.tabsInitialized === "true") return;
        tabContainer.dataset.tabsInitialized = "true";

        function switchTab(index) {
            tabs.forEach(tab => tab.classList.remove("active"));
            buttons.forEach(btn => btn.classList.remove("active"));

            tabs[index].classList.add("active");
            buttons[index].classList.add("active");
        }

        buttons.forEach((button, index) => {
            button.addEventListener("click", () => switchTab(index));
        });

        switchTab(0);
    });
}

const observer = new MutationObserver(mutations => {
    mutations.forEach(mutation => {
        mutation.addedNodes.forEach(node => {
            if (node.nodeType === 1 && node.classList.contains(".vtabs-wrapper")) {
                initTabs(node);
            }
        });
    });
});

observer.observe(document.body, { childList: true, subtree: true });

document.addEventListener("DOMContentLoaded", () => {
    document.querySelectorAll(".vtabs-wrapper").forEach(initTabs);
});
</script>

ВЕРСИЯ 2 (другие узлы)

Код:
<!-- текстовые поля вместо строк для ввода в профиле by Vandra  -->
<script>
document.addEventListener("DOMContentLoaded", function () {
    const profileContainer = document.getElementById("profile8");
    if (!profileContainer) return; 
    const profInputs = profileContainer.querySelectorAll("#fld2, #fld3, #fld4, #fld5");
    profInputs.forEach(profInput => {
        const profTextarea = document.createElement("textarea");
        for (let { name, value } of profInput.attributes) {
            profTextarea.setAttribute(name, value);
        }
        profTextarea.value = profInput.value;
        profInput.replaceWith(profTextarea);
    });
});
</script>

<!-- вкладки для ЛС без ID by Vandra  -->
<script>
function initTabs(container) {
    container.querySelectorAll(".vtabs-cont").forEach(tabContainer => {
        const buttons = tabContainer.querySelectorAll(".vtab-btn");
        const tabs = tabContainer.querySelectorAll(".vtab-content");

        if (!buttons.length || !tabs.length) return;
        if (tabContainer.dataset.tabsInitialized === "true") return;

        tabContainer.dataset.tabsInitialized = "true";

        function switchTab(index) {
            tabs.forEach(tab => tab.classList.remove("active"));
            buttons.forEach(btn => btn.classList.remove("active"));

            tabs[index].classList.add("active");
            buttons[index].classList.add("active");
        }

        buttons.forEach((button, index) => {
            button.addEventListener("click", () => switchTab(index));
        });

        switchTab(0);
    });
}

const observer = new MutationObserver(mutations => {
    mutations.forEach(mutation => {
        mutation.addedNodes.forEach(node => {
            if (node.nodeType !== 1) return;

            if (node.classList && node.classList.contains("vtabs-wrapper")) {
                initTabs(node);
            }

            const nestedWrappers = node.querySelectorAll?.(".vtabs-wrapper");
            nestedWrappers?.forEach(wrapper => {
                initTabs(wrapper);
            });
        });
    });
});

observer.observe(document.body, { childList: true, subtree: true });

document.querySelectorAll(".vtabs-wrapper").forEach(initTabs);
</script>
Код:
.vtab-content {
  display: none;
  padding: 10px;
  border: 1px solid #ccc;
}

.vtab-content.active {
  display: block;
}

.vtab-btn {
  padding: 5px 10px;
  margin-right: 5px;
  cursor: pointer;
  background: #eee;
  border: 1px solid #bbb;
  transition: background 0.3s;
}

.vtab-btn.active {
  background: #ccc;
  font-weight: bold;
}