<meta name="viewport" content="width=device-width, initial-scale=1.0">
background: gray url(Image/mosaico.jpg) repeat;
<link href="estilos.css" rel="stylesheet" type="text/css">
var f=document.getElementById("frm");
txt.value = "Ola "+txt.value;
var f=document.getElementById("frm");
var n1=document.getElementById("n1").value;
var n2=document.getElementById("n2").value;
var f=document.getElementById("frm");
var n1=document.getElementById("n1").value;
var n2=document.getElementById("n2").value;
function multiplicacao() {
var f=document.getElementById("frm");
var n1=document.getElementById("n1").value;
var n2=document.getElementById("n2").value;
var f=document.getElementById("frm");
var n1=document.getElementById("n1").value;
var n2=document.getElementById("n2").value;
function mostrarresultados() {
var f=document.getElementById("frm");
<input type="text" name="txtnome" placeholder="Introduza o seu nome">
<input id="enviar" type="button" value="Enviar" onClick="ola('Ola')">
<span>Introduza os numeros:</span><br>
<input type="text" size="2" name="n1" placeholder="n1"><br>
<input type="text" size="2" name="n2" placeholder="n2"><br><br>
<input type="button" value="+" onClick="soma()">
<input type="button" value="-" onClick="subtracao('')">
<input type="button" value="*" onClick="multiplicacao('')">
<input type="button" value="/" onClick="divisao('')"><br><br>
<input type="button" value="Limpar" onClick="limpar()"/>
<input type="button" value="Enviar" onClick="ola('Ola')">
<img id="mario1" src="Image/mario1.jpg" alt=""/>
<img id="mario2" src="Image/mario2.jpg" alt=""/>