TYPO3: dropdown login box (menu)

Question

I would like to create a dropdown login box in the menu. When users hover over "login" in the menu, it shows the login or register form. I found an example here: https://www.planet-sports.com/en/

I am quite new to TYPO3 so I don't know where I should start. Is there a way to do this with Typoscript only or should I modify the navbar with html and javascript? What is the best way to do this ?

EDIT: I am using a custom theme (not done by myself)

The Menu is called in a "header.html" file like this:

<nav class="collapse navbar-collapse navbar-main-collapse" role="navigation">
        <f:cObject typoscriptObjectPath="menu.navbar" />
    </nav>

Typoscript for the navbar:

    menu.navbar = HMENU
menu.navbar {
    entryLevel = 0
    excludeUidList = 112

    1 = TMENU
    1 {
        expAll = 1
        stdWrap.dataWrap = <ul class="nav navbar-nav colum-{register:count_menuItems}">|</ul>

        NO {
            htmlSpecialChars = 1
            wrapItemAndSub = <li id="navbar{field:uid}" class="first" >|</li> |*| <li id="navbar{field:uid}">|</li> |*| <li id="navbar{field:uid}" class="last navbar-right">|</li>
            wrapItemAndSub.insertData = 1
            ATagTitle.field = description // subtitle
        }

        ACT = 1
        ACT {
            htmlSpecialChars = 1
            wrapItemAndSub = <li id="navbar{field:uid}" class="first active">|</li> |*| <li id="navbar{field:uid}" class="active">|</li> |*| <li id="navbar{field:uid}" class="last active navbar-right">|</li>
            wrapItemAndSub.insertData = 1
            ATagTitle.field = description // subtitle
        }

        IFSUB = 1
        IFSUB {
            ATagTitle.field = description // subtitle
            wrapItemAndSub = <li id="navbar{field:uid}" class="dropdown first">|</li> |*| <li id="navbar{field:uid}" class="dropdown">|</li> |*| <li id="navbar{field:uid}" class="dropdown last">|</li>
            wrapItemAndSub.insertData = 1
            stdWrap.htmlSpecialChars = 1
            ATagParams = class="dropdown-toggle" data-toggle="dropdown" role="button" aria-haspopup="true" aria-expanded="false"
            linkWrap = |<span class="caret"></span>
            ATagBeforeWrap = 1
        }

        ACTIFSUB < .IFSUB
        ACTIFSUB = 1
        ACTIFSUB.wrapItemAndSub = <li id="navbar{field:uid}" class="dropdown first active">|</li> |*| <li id="navbar{field:uid}" class="dropdown active">|</li> |*| <li id="navbar{field:uid}" class="dropdown last active">|</li>
    }

    2 = TMENU
    2 {
        expAll = 1
        wrap = <ul class="dropdown-menu">|</ul>

        NO.htmlSpecialChars = 1
        NO.wrapItemAndSub = |*| <li class="odd">|</li> || <li class="even">|</li> |*|

        ACT = 1
        ACT.htmlSpecialChars = 1
        ACT.wrapItemAndSub = |*| <li class="odd active">|</li> || <li class="even active">|</li> |*|
    }

    3 = TMENU
    3 {
        expAll = 1
        wrap = <ul class="dropdown-submenu">|</ul>

        NO.htmlSpecialChars = 1
        NO.wrapItemAndSub = <li class="first">|</li> |*| <li>|</li> |*| <li class="last">|</li>

        ACT = 1
        ACT.htmlSpecialChars = 1
        ACT.wrapItemAndSub = <li class="first active">|</li> |*| <li class="active">|</li> |*| <li class="active last">|</li>
    }

    4 = TMENU
    4 {
        wrap = <ul class="dropdown-submenu-1">|</ul>

        NO.htmlSpecialChars = 1
        NO.wrapItemAndSub = <li class="first">|</li> |*| <li>|</li> |*| <li class="last">|</li>

        ACT = 1
        ACT.htmlSpecialChars = 1
        ACT.wrapItemAndSub = <li class="first active">|</li> |*| <li class="active">|</li> |*| <li class="active last">|</li>
    }
}

Answer 1

first of all: the visibility of a layer can be handled with CSS (even fade in/fade out or explode/implode). just put all content in a div which is included in the trigger div.
How you get your content into this div depends of the kind you build your page. fluid-template, marker-template, pure typoscript.
there are multiple ways to get the login form (and other content) into the div: create it by typoscript, get the content from a fix page, get the content from a special column which is inherited to all subpages (slide).

just be a little be more specific what your current configuration is, what you are familiar with and what you want to achieve.