Hugo-theme-stack/layouts/partials/sidebar/left.html

<aside class="sidebar left-sidebar sticky">
    <button class="hamburger hamburger--spin" type="button" id="toggle-menu" aria-label="{{ T `toggleMenu` }}">
        <span class="hamburger-box">
            <span class="hamburger-inner"></span>
        </span>
    </button>

    <header class="site-info">
        {{ with .Site.Params.sidebar.avatar }}
            <figure class="site-avatar">
                {{ $avatar := resources.Get (.) }}

                {{ if $avatar }}
                    {{ $avatarResized := $avatar.Resize "300x300" }}
                    <img src="{{ $avatarResized.RelPermalink }}" width="{{ $avatarResized.Width }}"
                        height="{{ $avatarResized.Height }}" class="site-logo" loading="lazy" alt="Avatar">
                {{ else }}
                    {{ errorf "Failed loading avatar from %q" . }}
                {{ end }}

                <span class="emoji">{{ $.Site.Params.sidebar.emoji }}</span>
            </figure>
        {{ end }}
        <h1 class="site-name"><a href="{{ .Site.BaseURL }}">{{ .Site.Title }}</a></h1>
        <h2 class="site-description">{{ .Site.Params.sidebar.subtitle }}</h2>
    </header>

    <ol class="menu" id="main-menu">
        {{ $currentPage := . }}
        {{ range .Site.Menus.main }}
        {{ $active := or (eq $currentPage.Title .Name) (or ($currentPage.HasMenuCurrent "main" .) ($currentPage.IsMenuCurrent "main" .)) }}

        <li {{ if $active }} class='current' {{ end }}>
            <a href='{{ .URL | relURL }}'>
                {{ if .Pre }}
                    {{ partial "helper/icon" .Pre }}
                {{ end }}
                <span>{{- .Name -}}</span>
            </a>
        </li>
        {{ end }}
    </ol>
</aside>