ボーダーラインの太さ、線種、色をまとめて指定します。

.sample-solid {
    border: 1px solid gray;
    width: 80px;
    height: 40px;
    margin: 0em 0em 0em 1em;
}
.sample-dashed {
    border: 1px dashed gray;
    width: 80px;
    height: 40px;
    margin: 0em 0em 0em 1em;
}
.sample-dotted {
    border: 1px dotted gray;
    width: 80px;
    height: 40px;
    margin: 0em 0em 0em 1em;
}
.sample-10 {
    border: 10px solid #993333;
    width: 80px;
    height: 40px;
    margin: 0em 0em 0em 1em;
}

<h5>1px solid</h5>
<div class="sample-solid"></div>
<h5>1px dashed</h5>
<div class="sample-dashed"></div>
<h5>1px dotted</h5>
<div class="sample-dotted"></div>
<h5>10px solid</h5>
<div class="sample-10"></div>

• http://www.w3.org/TR/CSS1/#border
• http://www.w3.org/TR/CSS2/box.html#border-shorthand-properties
• http://www.w3.org/TR/css3-background/#the-border-shorthands4
• https://developer.mozilla.org/ja/docs/Web/CSS/border
• http://caniuse.com/#search=css%202.1%20properties