Right/left sided triangle in css - css

Question

Hi i am trying to make the following:
They triangles should be about 40% in height of the container, and 50% in width, so they meet in the middle.
I have been trying to make something similar.. but unsuccessfull so far..
And looking around, i have found nothing i could use so far.
my code:
div {
height: 373px;
width: 0px;
margin: 26px;
display: inline-block;
}
.left {
border-bottom: 100px solid #ff0;
border-left: 320px solid transparent;
}
.right {
border-bottom: 100px solid #f00;
border-right: 320px solid transparent;
}
header {
border: 2px solid black;
width: 50%;
height: 500px;
}
<header>
<div class="right"></div>
<div class="left"></div>
</header>
hoping for someone smarter than me to see where i should go from here...

Answer 1

Use background coloration like below:
.box {
height:300px;
background:
/* Right bottom triangle*/
linear-gradient(to bottom right,transparent 49.5%,blue 50%) bottom right,
/* left bottom triangle*/
linear-gradient(to bottom left ,transparent 49.5%,red 50%) bottom left ,
yellow;
background-size:50% 40%; /* Width height*/
background-repeat:no-repeat;
}
<div class="box">
</div>
Related answer for more details: How do CSS triangles work?
Another idea with pseudo elements (that you can replace with common elements) in case you want to have different elements.
.box {
height: 300px;
background: yellow;
position: relative
}
.box:before,
.box:after {
content: "";
position: absolute;
height: 40%;
width: 50%;
bottom: 0;
}
.box:before {
left: 0;
background: linear-gradient(to bottom left, transparent 49.5%, red 50%);
}
.box:after {
right: 0;
background: linear-gradient(to bottom right, transparent 49.5%, blue 50%);
}
<div class="box">
</div>

Answer 2

Since you need percent values, you can use clip-path. Beware that it may not be supported fully on some browser https://caniuse.com/#feat=css-clip-path and for some you may need prefixes (e.g. -webkit-clip-path)
.wrap {
height: 200px;
width: 100%;
position: relative;
background: #333;
}
.triangle {
background: red;
clip-path: polygon(0 40%, 0% 100%, 100% 100%);
position: absolute;
left: 0;
bottom: 0;
top: 0;
width: 50%;
}
.triangle.tr-right {
left: auto;
right: 0;
clip-path: polygon(100% 40%, 0% 100%, 100% 100%);
}
<div class="wrap">
<div class="triangle tr-left"></div>
<div class="triangle tr-right"></div>
</div>
JSFiddle
Clip-path created with Clippy

Answer 3

* {
box-sizing: border-box;
}
.triangular-pointer-box {
display: flex;
align-items: center;
background: #161616;
padding: 20px;
padding-left: 120px;
height: 200px;
position: relative;
width: 80%;
}
.triangular-pointer-box > h3 {
color: #fff;
}
.triangular-pointer-box:after {
content: "";
width: 0;
height: 0;
border-top: 100px solid transparent;
border-bottom: 100px solid transparent;
border-left: 100px solid #161616;
position: absolute;
right: -100px;
top: 0;
}
.triangular-pointer-box:before {
content: "";
width: 0;
height: 0;
border-top: 100px solid transparent;
border-bottom: 100px solid transparent;
border-left: 100px solid #ffffff;
position: absolute;
left: 0;
top: 0;
}
<div class="triangular-pointer-box">
<h3>Title goes here</h3>
</div>