Exemple de code de la propriété CSS animation-fill-mode.

<style>
.bloc{ border:1px solid #666; width:90%; margin-bottom:5px; padding:5px; 
 animation-duration : 10s; 
 animation-delay : 3s; 
}

#animation-fill-mode-none {
 animation-name : animation; 
 animation-fill-mode : none; 
}

#animation-fill-mode-forwards {
 animation-name : animation; 
 animation-fill-mode : forwards; 
}

#animation-fill-mode-backwards{
 animation-name : animation; 
 animation-fill-mode : backwards; 
}

#animation-fill-mode-both{
 animation-name : animation; 
 animation-fill-mode : both; 
}

@keyframes animation{
 from { width : 90% } 
 to { width : 100px }
}
</style>
<div class="bloc" id="animation-fill-mode-none"> animation-fill-mode : none </div>
<div class="bloc" id="animation-fill-mode-forwards"> animation-fill-mode : forwards </div>
<div class="bloc" id="animation-fill-mode-backwards"> animation-fill-mode : backwards </div>
<div class="bloc" id="animation-fill-mode-both"> animation-fill-mode : both </div>