@JordiNebot answer is where I think we'd like to eventually land, but clip-path
hasn't been completely included yet. If you want to make sure it runs well everywhere, I would do something along the lines of the following. Create two triangles built from the middle out-ward well beyond what you would expect to need, then place them in absolute position at the bottom middle of the div containing the image.
It's considerably more work, but it will work better across all platforms.
.main {
position: relative;
overflow: hidden;
width: 100%;
}
.leftArrow {
position: absolute;
width: 0;
right: 50%;
height: 0;
bottom: 4px;
border-right: 500px solid transparent;
border-bottom: 100px solid black;
}
.rightArrow {
position: absolute;
left: 50%;
bottom: 4px;
width: 0;
height: 0;
border-left: 500px solid transparent;
border-bottom: 100px solid black;
}
img {
max-width: 100%;
width: 100%;
}
<div class="main">
<img src="https://loremflickr.com/1280/720">
<div class="leftArrow"></div>
<div class="rightArrow"></div>
</div>