<script>
  function klik(x)
  {
    var c1 = document.getElementById("c1");
    var l1 = document.getElementById("l1");
    var t1 = document.getElementById("t1");
    //
    t1.style.fontSize = c1.value+"%";
    //
    if (x == 1) t1.style.color = "red";
    if (x == 2) t1.style.color = "green";
    if (x == 3) t1.style.color = "blue";
    //
    if (l1.value == 0) t1.style.fontStyle = "normal";
    if (l1.value == 1) t1.style.fontStyle = "italic";
  }
</script>

<form>
<p>Podaj rozmiar tekstu w procentach: <input type="text" id="c1" value="150" onkeyup="klik(1)">%</p>

<p><select id="l1">
  <option value="0">prosty</option>
  <option value="1">pochylony</option>
</select></p>
</form>

<p>Jakim kolorem sformatowac tekst?</p>

<p><button style="background-color: red;" onclick="klik(1)">-</button>
<button style="background-color: green;" onclick="klik(2)">-</button>
<button style="background-color: blue;" onclick="klik(3)">-</button></p>

<p id="t1">To jest przykład paragrafu</p>