一、效果图 

二、代码

html

<div class="rectangle">AC/DC</div>

css

/* 图形 */
.rectangle {
    position: relative;
    width: 50px;
    height: 20px;
    background-color: #3498db;
    color: white;
} 
.rectangle:before {
    content: '';
    position: absolute;
    top: 0;
    left: 50px;
    width: 0;
    height: 0;
    border-top: 10px solid transparent;
    border-left: 10px solid #3498db;
    border-bottom:10px solid transparent;
}