Edit in JSFiddle

<div class="triangle-border top"> 
 Merhaba Dünya!
</div>

.triangle-border {
            position: relative;
            padding: 15px;
            margin: 1em 0 3em;
            border: 5px solid #5a8f00;
            color: #333;
            background: #fff;
            -webkit-border-radius: 10px;
            -moz-border-radius: 10px;
            border-radius: 10px;
        }
            .triangle-border.top:before {
                top: -20px;
                bottom: auto;
                right: 40px;
                border-width: 0 20px 20px;
            }
            .triangle-border:before {
                content: "";
                position: absolute;
                bottom: -20px;
                left: 40px;
                border-width: 20px 20px 0;
                border-style: solid;
                border-color: #5a8f00 transparent;
                display: block;
                width: 0;
            }
            .triangle-border.top:after {
                top: -13px;
                bottom: auto;
                right: 47px;
                border-width: 0 13px 13px;
            }
            .triangle-border:after {
                content: "";
                position: absolute;
                bottom: -13px;
                left: 47px;
                border-width: 13px 13px 0;
                border-style: solid;
                border-color: #fff transparent;
                display: block;
                width: 0;
            }