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Oct 30, 2025
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Added pure HTML & CSS 3D triangle design #950

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138 changes: 138 additions & 0 deletions 3D Triangle/triangle-3d.html
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<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width,initial-scale=1" />
<title>3D Triangle (CSS only)</title>
<style>
:root{
--size: 260px; /* width of triangle */
--depth: 48px; /* extrusion depth */
--bg: #071029;
--face: #06b6d4;
--face-2: #038aa6;
--shadow: rgba(2,6,23,0.6);
}

html,body{
height:100%;
margin:0;
font-family: system-ui, Arial;
background: linear-gradient(180deg, #03243a 0%, var(--bg) 100%);
display:grid;
place-items:center;
color:#fff;
}

.stage{
perspective: 900px;
}

/* container that preserves 3D children */
.prism {
width: var(--size);
height: calc(var(--size) * 0.86); /* approx triangle height */
position: relative;
transform-style: preserve-3d;
transform: rotateX(16deg) rotateY(-16deg);
transition: transform .45s cubic-bezier(.2,.9,.2,1);
filter: drop-shadow(0 18px 30px var(--shadow));
}

.stage:hover .prism{
transform: rotateX(6deg) rotateY(18deg) translateZ(8px);
}

/* front & back triangular faces */
.face {
position: absolute;
inset: 0;
width: 100%;
height: 100%;
-webkit-clip-path: polygon(50% 0%, 0% 100%, 100% 100%);
clip-path: polygon(50% 0%, 0% 100%, 100% 100%);
backface-visibility: hidden;
}

.face.front {
background: linear-gradient(180deg, var(--face) 0%, var(--face-2) 100%);
transform: translateZ(calc(var(--depth) / 2));
box-shadow: 0 6px 18px rgba(3,12,30,.45) inset;
}

.face.back {
background: linear-gradient(180deg, var(--face-2) 0%, var(--face) 100%);
transform: rotateY(180deg) translateZ(calc(var(--depth) / 2));
opacity: 0.96;
}

/* side panels: three trapezoids connecting front & back */
.side {
position: absolute;
width: 100%;
height: 100%;
transform-origin: center;
backface-visibility: hidden;
}

/* left side panel */
.side.left {
/* create a quadrilateral covering left edge */
-webkit-clip-path: polygon(50% 0%, 0% 100%, 0% 100%, 50% 0%);
clip-path: polygon(50% 0%, 0% 100%, 0% 100%, 50% 0%);
background: linear-gradient(90deg, rgba(0,0,0,.12), rgba(0,0,0,0));
transform: rotateY(90deg) translateX(calc(var(--size) / -2)) translateZ(calc(var(--depth) / -2));
opacity: 0.95;
}

/* right side panel */
.side.right {
-webkit-clip-path: polygon(50% 0%, 100% 100%, 100% 100%, 50% 0%);
clip-path: polygon(50% 0%, 100% 100%, 100% 100%, 50% 0%);
background: linear-gradient(90deg, rgba(0,0,0,0), rgba(0,0,0,.12));
transform: rotateY(-90deg) translateX(calc(var(--size) / 2)) translateZ(calc(var(--depth) / -2));
opacity: 0.95;
}

/* bottom side panel (base thickness) */
.side.bottom {
/* a thin band along base */
-webkit-clip-path: polygon(0% 100%, 50% 100%, 100% 100%, 100% 100%);
clip-path: polygon(0% 100%, 50% 100%, 100% 100%, 100% 100%);
background: linear-gradient(180deg, rgba(0,0,0,.12), rgba(255,255,255,0.02));
transform: rotateX(90deg) translateY(calc(var(--size) * 0.43)) translateZ(calc(var(--depth) / -2));
height: calc(var(--depth));
top: auto;
bottom: -1px;
}

/* simple label */
.label {
margin-top: 18px;
text-align: center;
font-size: 14px;
opacity: .85;
}

/* small responsive tweak */
@media (max-width:520px){
:root{ --size: 200px; --depth: 36px; }
}
</style>
</head>
<body>
<div class="stage">
<div class="prism" aria-hidden="true">
<div class="face front"></div>
<div class="face back"></div>

<!-- side panels: visual depth only -->
<div class="side left"></div>
<div class="side right"></div>
<div class="side bottom"></div>
</div>

<div class="label">Pure HTML & CSS — 3D triangle (extruded)</div>
</div>
</body>
</html>