change theme-switch from 'a' to 'button'

and refactor

layouts/partials/header.html

@@ -61,7 +61,7 @@
             {{- end }}
             <span class="logo-switches">
                 {{- if (not .Site.Params.disableThemeToggle) }}
-                <a id="theme-toggle" accesskey="t" title="(Alt + T)">
+                <button id="theme-toggle" accesskey="t" title="(Alt + T)">
                     <svg id="moon" xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24"
                         fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round"
                         stroke-linejoin="round">
@@ -80,7 +80,7 @@
                         <line x1="4.22" y1="19.78" x2="5.64" y2="18.36"></line>
                         <line x1="18.36" y1="5.64" x2="19.78" y2="4.22"></line>
                     </svg>
-                </a>
+                </button>
                 {{- end}}
                 {{ $lang := .Lang}}
                 {{ $separator := or .Title (not .Site.Params.disableThemeToggle)}}