Promokit Helpdesk Alysum

I am tying to use css to do some smalls changes… but I haven´t got sucess…

I do a table that works like that….

HTML

---

<table class=”tablapx”>
<tbody>
<tr><th width=”10%”></th><th width=”30%”>
<……..>

</tbody>
</table>

CSS

---

table.tablaga th {

  text-align: center;
  vertical-align: middle;
  background-color: #81BEF7;
  color: white;

}

But i would like to change for example in diferente text color and size . I write
html. I am trying evething but it doesn´t work.

HTML

<p class=”center”>text example </p>

CSS p.center {

  text-align: center;
  color: red;

}

I am try to change a specific h2 or h3 and I can´t

Tanks.