img {
max- 100%;
height: auto;
}
<img src="http://www.runoob.com/wp-content/uploads/2016/04/trolltunga.jpg" alt="Norway" width="1000" height="300">
img {
max- 100%;
height: auto;
}
<img src="http://www.runoob.com/wp-content/uploads/2016/04/trolltunga.jpg" alt="Norway" width="1000" height="300">