I need to use an item, in this case img, in the same div class but with different definitions.

Example:

```
section .row img {
    margin: 0 0 30px;
    width: 100%;
    border: 4px solid #18a00e;
}

section .row img {
    margin: 0 0 30px;
    border: 4px solid #18a00e;
    max-height: 300px;
}

```

How can I create and use this two definitions without the last one overwriting the former?
Thank you.

Later edit (for more info):

```
//this is the html code scenario 1 where I need the width: 100%//
<section class="container">
    <div class="row">
        <figure class="col-lg-4 col-md-4 col-sm-4 col-xs-4">
           <img src="img/m3.jpg"/>
        </figure>
    </div>
</section>

//this is the html code for scenario 2, where I need max-height: 300px//
<section class="jumbotron">
    <div class="unlockedl">
        <div class="row">
            <img src="img/pm1.jpg"/>
        </div>
    </div>
</section>

```