placeholder: placeholder="Name eingeben"
input type="email"
required: <input type="checkbox" name="agb" required> 
min=0: <input type="number" id="so" name="sonntag" placeholder="0" min="0" >


  <form id="kaufen" action="kasse.php" method="post">
   <fieldset>
     <legend>Tickets kaufen</legend>
     <input type="number" id="sa" name="samstag" placeholder="0" min="0" >
     <label for="sa">Samstag 5€/Ticket</label><br>
     <input type="number" id="so" name="sonntag" placeholder="0" min="0" >
     <label for="so">Sonntag 5€/Ticket</label><br>
     <input type="number" id="kombi" name="kombiticket" placeholder="0" min="0" >
     <label for="so">Kombiniert 7€/Ticket</label><br>
     <input type="checkbox" id="agb" name="agb" required>
     <label for="agb">Ich bin mit den <a href="agb.html" target="_blank">AGB</a> einverstanden</label>
     <button>Zur&nbsp;Kasse</button> <button type="reset">Zurücksetzen</button>
     </fieldset>
     </form>
     <form id="newsletter" action="news.php" method="post">
     <fieldset>
     <legend>Newsletter abonnieren</legend>
     <label for="email">Email: </label><input type="email" id="email" name="email" required>
     <button>Newsletter abonnieren</button>
     </fieldset>
  </form>