How to create a transparent triangle with border using CSS?

Question

How can I create the following shape with CSS?

Enter image description here

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.

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. — Spudley
– Spudley, Commented Apr 26, 2013 at 8:06

Maen · Accepted Answer · 2019-05-31 13:25:16Z

17

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

edited May 31, 2019 at 13:25

answered Apr 26, 2013 at 8:13

Maen

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3 Comments

Manoz Over a year ago

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

Mr. Alien Over a year ago

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

Maen Over a year ago

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

3 revs, 2 users 58% · Accepted Answer · 2023-07-02 17:45:05Z

11

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/

edited Jul 2, 2023 at 17:45

community wiki

3 revs, 2 users 58%
Samuel Liew

Comments

Temani Afif · Accepted Answer · 2024-08-13 22:35:21Z

New answer

In addition to the below answer using gradients, I also have an online collection 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?

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?
@klewis 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

Sowmya · Accepted Answer · 2013-04-26 07:52:30Z

7

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

edited Apr 26, 2013 at 7:52

answered Apr 26, 2013 at 7:46

Sowmya

27k21 gold badges102 silver badges137 bronze badges

2 Comments

Sowmya Over a year ago

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

Spudley Over a year ago

+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".

Temani Afif · Accepted Answer · 2019-06-06 19:41:54Z

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>

enxaneta · Accepted Answer · 2019-06-15 10:07:18Z

3

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>

edited Jun 15, 2019 at 10:07

enxaneta

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answered Apr 26, 2013 at 8:01

Imperative

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Comments

enxaneta · Accepted Answer · 2019-06-15 10:05:16Z

2

    .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.

edited Jun 15, 2019 at 10:05

enxaneta

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answered Apr 26, 2013 at 7:47

sakthi

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1 Comment

William Over a year ago

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

G-Cyrillus · Accepted Answer · 2021-07-20 15:38:14Z

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/

NNH · Accepted Answer · 2018-09-12 19:24:09Z

0

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;

}

answered Sep 12, 2018 at 19:24

NNH

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