When I paste text with multiple lines into my <input type="text"> this happens:

The the text normally stays in one line in the middle when I paste it onto another website:

My CSS :
.textbox {
padding:0 5px;
height:30px;
background:#FDFDFD;
line-height:28px;
width:250px;
border:1px solid #D2D2D2;
}
@media screen and (-webkit-min-device-pixel-ratio:0) {
.textbox { line-height:13px; }
}
HTML:
<input type="text" class="textbox">
I am just curious on why this happens. I do not use <input type="text"> for this purpose.
Don’t do it.
<input type="text">is for single-line input. In authoring, usetextareato allow multiple lines.