How to create a transparent triangle with border using CSS?

Question

How can I create the following shape with CSS?

I tried this to be a solution:

.triangle:after {
  position: absolute;
  content: "";
  width: 0;
  height: 0;
  margin-top: 1px;
  margin-left: 2px;
  border-left: 10px solid transparent;
  border-right: 10px solid transparent;
  border-bottom: 10px solid white;
}

.triangle:before {
  position: absolute;
  content: "";
  width: 0;
  height: 0;
  border-left: 12px solid transparent;
  border-right: 12px solid transparent;
  border-bottom: 12px solid black;
}

<div class="triangle"></div>

You can see it working at Triangle. This is working, but with a trick of borders. Is there another way it could be done?

Using SVG vectors this can be done easily, but I don't want to go that lengthy way.

Ameeameer

Only with CSS ? And with transparent body? – Blockhead

apps.eky.hk/css-triangle-generator – Atrocity

hedgerwow.appspot.com/demo/arrows – Atrocity

jonrohan.me/guide/css/creating-triangles-in-css – Atrocity

@Bigood: Yeah only with CSS, because i know Using SVG graphics is pretty lengthy. – Ameeameer

@Ameeameer Do you want only borders of your triangle? – Blockhead

@Bigood: yes! I think giving strokes will do that? isn't it? – Ameeameer

In all seriousness, SVG is the most appropriate solution here. Yes you can acheive some very clever things with CSS, but SVG is designed for drawing arbitrary shapes; CSS isn't. The irony is that you're discounting SVG because you think it's hard, but really it isn't. It's honestly pretty easy. Sure SVG can get complex if you're drawing complex shapes, but a basic triangle is not complex; it takes less SVG code to draw a triangle than CSS, and it's easier to understand the code too. – Mercuri

Answer 1

I've found a webkit-only solution, using the ▲ character:

.triangle {
  -webkit-text-stroke: 12px black;
  color: transparent;
  font-size: 200px;
}

<div class="triangle">&#9650;</div>

Extras:

• CanIUse reference for text-stroke - all major browsers covered as of 2019
• CSS-tricks article
• Useful HTML shapes

Blockhead

@Bigood: This is finest solution i get in this question & tricky ;) – Ameeameer

@Ameeameer Even samuel was good, he got my upvote, as that will be cross browser where this is not, but this is real cool – Mariahmariam

@softvar Sure, but I won't post it here. Please ask a new question, and I'll try to answer it quickly. – Blockhead

Answer 2

CSS-border version:

.triangle {
  position: relative;
  width: 0;
  border-bottom: solid 50px black;
  border-right: solid 30px transparent;
  border-left: solid 30px transparent;
}

.triangle .empty {
  position: absolute;
  top: 9px;
  left: -21px;
  width: 0;
  border-bottom: solid 36px white;
  border-right: solid 21px transparent;
  border-left: solid 21px transparent;
}

<div class="triangle">
  <div class="empty"></div>
</div>

Adding a white triangle inside the black one: http://jsfiddle.net/samliew/Hcfsx/

Prolamine

Answer 3

New answer

In addition to the below answer using gradients, I also have an online generator for triangle shapes where you can get some border-only triangles: https://css-generators.com/triangle-shapes/

---

Old answer

Here is an idea using multiple background and linear-gradient:

.triangle {
  width:100px;
  height:100px;
  
  background:
    /* Left side */
    linear-gradient(to bottom left,
      transparent 49.5%,#000 50% calc(50% + 10px),
      transparent calc(50% + 11px)) right/50% 100%,
    /* right side */
    linear-gradient(to bottom right,
      transparent 49.5%,#000 50% calc(50% + 10px),
      transparent calc(50% + 11px)) left/50% 100%,
    /* bottom side*/
    linear-gradient(#000,#000) bottom/calc(100% - 20px) 10px;
  background-repeat:no-repeat;
}

<div class="triangle"></div>

You can consider CSS variables to easily adjust the shape:

.triangle {
  --t:10px;  /* Thickness */
  --c:black; /* Color */

  width:100px;
  height:100px;
  display:inline-block;
  
  background:
    /* Left side */
    linear-gradient(to bottom left,
      transparent 49.5%,var(--c) 50% calc(50% + var(--t)),
      transparent calc(50% + var(--t) + 1px)) right/50% 100%,
    /* right side */
    linear-gradient(to bottom right,
      transparent 49.5%,var(--c) 50% calc(50% + var(--t)),
      transparent calc(50% + var(--t) + 1px)) left/50% 100%,
    /* bottom side*/
    linear-gradient(var(--c),var(--c)) bottom/calc(100% - 2*var(--t)) var(--t);
  background-repeat:no-repeat;
}

body {
 background:pink;
}

<div class="triangle"></div>

<div class="triangle" style="--t:5px;--c:blue;width:150px"></div>

<div class="triangle" style="--t:8px;--c:red;height:150px"></div>

<div class="triangle" style="--t:15px;--c:green;width:80px"></div>

A different syntax with less gradient:

.triangle {
  --t:10px;  /* Thickness */
  --c:black; /* Color */

  width:100px;
  height:100px;
  display:inline-block;
  border:var(--t) solid transparent;
  border-bottom-color:var(--c);
  background:
    /* Left side */
    linear-gradient(to bottom left,
      transparent 49.5%,var(--c) 50% calc(50% + var(--t)),
      transparent calc(50% + var(--t) + 1px)) right,
    /* right side */
    linear-gradient(to bottom right,
      transparent 49.5%,var(--c) 50% calc(50% + var(--t)),
      transparent calc(50% + var(--t) + 1px)) left;
  background-size:50% 100%;
  background-origin:border-box;
  background-repeat:no-repeat;
}

body {
 background:pink;
}

<div class="triangle"></div>

<div class="triangle" style="--t:5px;--c:blue;width:150px"></div>

<div class="triangle" style="--t:8px;--c:red;height:150px"></div>

<div class="triangle" style="--t:15px;--c:green;width:80px"></div>

You can consider the same idea to create a rectangle triangle:

.triangle {
  --t:10;  /* Thickness */
  --c:black; /* Color */

  width:100px;
  height:100px;
  display:inline-block;
  border:calc(var(--t)*1px) solid transparent;
  border-image:
    linear-gradient(to bottom left,
      transparent 49.5%,var(--c) 50%) var(--t);
  background:
    /* Left side */
    linear-gradient(to bottom left,
      transparent 49.5%,var(--c) 50% calc(50% + var(--t)*1px),
      transparent calc(50% + var(--t)*1px + 1px));
  background-origin:border-box;
  background-repeat:no-repeat;
}

body {
 background:pink;
}

<div class="triangle"></div>

<div class="triangle" style="--t:5;--c:blue;width:150px"></div>

<div class="triangle" style="--t:8;--c:red;height:150px"></div>

<div class="triangle" style="--t:15;--c:green;width:80px"></div>

If you want an equilateral triangle simply keep a ratio bettween the width/height using the initial code

.triangle {
  --t:10px;  /* Thickness */
  --c:black; /* Color */

  width:100px;
  display:inline-block;
  border:var(--t) solid transparent;
  border-bottom-color:var(--c);
  background:
    /* Left side */
    linear-gradient(to bottom left,
      transparent 49.5%,var(--c) 50% calc(50% + var(--t)),
      transparent calc(50% + var(--t) + 1px)) right,
    /* right side */
    linear-gradient(to bottom right,
      transparent 49.5%,var(--c) 50% calc(50% + var(--t)),
      transparent calc(50% + var(--t) + 1px)) left;
  background-size:50% 100%;
  background-origin:border-box;
  background-repeat:no-repeat;
}

.triangle:before {
  content:"";
  display:block;
  padding-top:86.6%;
}

body {
 background:pink;
}

<div class="triangle"></div>

<div class="triangle" style="--t:5px;--c:blue;width:150px"></div>

<div class="triangle" style="--t:8px;--c:red;width:50px"></div>

<div class="triangle" style="--t:15px;--c:green;width:80px"></div>

Related answer for more details about the calculation: How do CSS triangles work?

Prompter

Why does this solution turn into a solid black triangle if the width and the height is set to a low number like 30px? What would be the correction in that instance? – Marylandmarylee

@Marylandmarylee if you set a width/height that is smaller than the twice the border thickness then you have no room for a space inside and you will end with a solid triangle – Prompter

Answer 4

Try using SVG

<svg xmlns="http://www.w3.org/2000/svg" version="1.1">
  <polygon points="200,10 250,190 160,210"
  style="fill:lime;stroke:purple;stroke-width:1"/>
</svg>

Here is the tutorial

Eblis

@Bigood That wasn't mentioned in question. My answer is older than his comment – Eblis

+1 because SVG is far a more appropriate solution even if it isn't what the OP actually asked for. Plus the OP is obviously mistaken about SVG -- the answer given here can hardly be described as "lengthy". – Mercuri

Answer 5

You can use the method I described here : How does this CSS triangle shape work? with a rotated pseudo element. You can then add a border to the rotated pseudo element to create the effect you are looking for.

You can also use this technique to display the triangle with borders over an image, gradient or any non plain backgrounds :

DEMO

.tr{
  width:40%;
  padding-bottom: 28.28%; /* = width / sqrt(2) */
  position:relative;
  border-bottom: 6px solid rgba(0,0,0,0.8);
  border-right: 6px solid transparent;
  border-left: 6px solid transparent;
  overflow:hidden;
}
.tr:before{
  content:'';
  position:absolute;
  bottom:0; left:0;
  width:100%; height:100%;
  border-top:6px solid rgba(0,0,0,0.8);
  border-left:6px solid rgba(0,0,0,0.8);
  
  -moz-box-sizing:border-box;
  box-sizing:border-box;
    
  -webkit-transform-origin:0 100%;
  -ms-transform-origin:0 100%;
  transform-origin:0 100%;
    
  -webkit-transform: rotate(45deg);
  -ms-transform: rotate(45deg);
  transform: rotate(45deg);
}


/* FOLLOWING JUST FOR THE DEMO */
body{background:url('https://picsum.photos/id/100/1000/1000');background-size:cover;}

<div class="tr"></div>

Hapte

Answer 6

Consider using the <canvas> element. I build a simple triangle on jsfiddle - nothing fancy, yet.

    var canvas = document.getElementById('myCanvas');
    var context = canvas.getContext('2d');

    context.beginPath();
    context.moveTo(10, 0);
    context.lineTo(20, 20);
    context.lineTo(0, 20);
    context.closePath();
    context.fill();

<canvas id="myCanvas" width="20" height="20"></canvas>

At

Answer 7

    .triangle{
        width:0;
        border-bottom:solid 30px black;
        border-right:solid 30px transparent;
        border-left:solid 30px transparent;
    }

    <div class="triangle">
    </div>

This will be a triangle pointed towards the top. Don't specify the border to the side where you need it to be pointed.

The above is an equilateral triangle. Remove border-left to make it a right-angled triangle.

Drawknife

The triangle in question is a hollow one, this is solid – Sulfuric

Answer 8

clip-path could also be considered:

html {
  /* init size and shape to the triangle*/
  --base: 155px;
  --ratio: 1;
  /* try too 0.71*/
  ;
}

[data-triangle] {
  width: var(--base);
  height: calc(var(--base) * var(--ratio));
  clip-path: polygon( 0 100%, 50% 0, 100% 100%, 94% 96%, 50% 8%, 6% 96%, 96% 96%, 100% 100%);
  background: gray;
}


/* demo makup */

html {
  display: grid;
  min-height: 100vh;
}

body {
  background: repeating-linear-gradient(45deg, silver 0, #444, gold, blue, lime, tomato, purple, gray 5em) 0 0 / 100% 100%;
  margin: auto;
  text-align: center;
  box-shadow: inset 0 0 0 100vw rgba(0, 0, 0, 0.5), 0 0 0 100vw rgba(0, 0, 0, 0.5);
  color:gray
}

[data-triangle] {
  transition: 1s;
}

body:hover [data-triangle]{
  background: black;
}

body:hover {
  filter: drop-shadow(0 0 1px gold)drop-shadow(0 0 1px white)drop-shadow(0 0 1px white)drop-shadow(0 0 1px white)drop-shadow(0 0 1px white)drop-shadow(0 0 10px white);
  /*make that triangle obvious over that funny gradient*/
  color: transparent;
  box-shadow: 0 0;
}


}

<div data-triangle></div>
hover to highlight

to help you create your clip-path, you can use this online tool https://bennettfeely.com/clippy/

Rachael

Answer 9

I found a nice solution, a bit tricky but for me it was the most easy way to do it: link to code-pen

.triangle {
position: absolute;
margin: auto;
top: -70px;
left: 0;
right: 0;
width: 137px;
height: 137px;
transform: rotate(45deg);
-webkit-transform: rotate(45deg);
-moz-transform: rotate(45deg);
-o-transform: rotate(45deg);
-ms-transform: rotate(45deg);
border-right: 4px solid #e74c3c;
border-bottom: 4px solid #e74c3c;

}

Ferriter