.a {
margin: 0 auto 1em;
border-style: solid;
border-width: thin;
border-color: #ff0000;
width: 500px;
text-align: center;
background: #ffffff;
}

.b {
margin: 0 auto 1em;
border-style: solid;
border-width: thin medium;
border-color: #ff0000 #0000ff;
width: 500px;
text-align: center;
background: #ffffff;
}

.c {
margin: 0 auto 1em;
border-style: solid;
border-width: thin medium thick;
border-color: #ff0000 #0000ff #008000;
width: 500px;
text-align: center;
background: #ffffff;
}

.d {
margin: 0 auto 1em;
border-style: solid;
border-width: thin medium thick 15px;
border-color: #ff0000 #0000ff #008000 #ffcc00;
width: 500px;
text-align: center;
background: #ffffff;
}