modmii.github.io/Support/Guide/side_spoiler_script.001

<script>
    let tabcontent = document.getElementsByClassName("blanktabcontent");
    let tablinks = document.getElementsByClassName("tablinks");

    function openTab(evt, tabName) {
        let element;

        for (element of tabcontent) {
            element.style.display = "none";
        }

        for (element of tablinks) {
            element.className = element.className.replace("btn--primary", "btn--info");
            if (!element.className.includes('btn--info'))
                element.className += " btn--info";
        }

        document.getElementById(tabName).style.display = "block";
        evt.currentTarget.className = evt.currentTarget.className.replace("btn--info", "btn--primary");
    }

    // Get the element with id="defaultOpen" and click on it
    document.getElementById("defaultOpen").click();
</script>