hugo-simpleIntro/layouts/404.html

{{ define "main" }}
    <div>
        <div id="mainBG" style="background-image: url('{{ if $.Site.Params.mainbg }}{{ $.Site.Params.mainbg }}{{ else }}https://picsum.photos/1920/1080{{ end }}');">

            {{ partial "utilities/wave"}}

            <div class="centerAll title font-bold text-center">
               <h1>404 - Not found</h1>
            </div>
        </div>
    </div>
{{ end }}