Why Does My Horizontally Centered Triangle Pointer Shift During Resizing?

Horizontal Centering of Triangle Pointer Encountering Issues During Screen Resizing

Problem Statement

The user intends to horizontally center a triangle pointer within a container element. While successful in certain window sizes, the pointer shifts out of alignment when the window is resized.

Solution

Understanding the Issue:

The initial attempt to center the pointer with left: 48% positions the pointer based on its left edge. This approach does not account for the element's width, resulting in misalignment when the window size changes.

Using transform to Achieve Centering:

To properly center the triangle, it's recommended to use the transform property:

.triangle {
   position: absolute;
   left: 50%;
   transform: translate(-50%,0);
}

This rule shifts the triangle's position by 50% of its width, effectively centering it within the container.

Combining transform with Rotation:

In this specific scenario, the triangle element also has a transform: rotate(45deg) applied. However, CSS cascade rules override the first transform with the second, preventing the horizontal centering.

To address this, chain the transform functions:

.container::before {
    left: 50%;
    transform: translate(-50%,0) rotate(45deg);
}

Multiple transform functions can be used together, applying in the order they are listed. In this case, translate is applied first, followed by rotate.

Complete Code Snippet:

body {
    background: #333333;
}

.container {
    width: 98%;
    height: 80px;
    line-height: 80px;
    position: relative;
    top: 20px;
    min-width: 250px;
    margin-top: 50px;
}

.container-decor {
    border: 4px solid #C2E1F5;
    color: #fff;
    font-family: times;
    font-size: 1.1em;
    background: #88B7D5;
    text-align: justify;
}

.container::before {
    top: -33px;
    left: 50%;
    transform: translate(-50%,0) rotate(45deg);
    position: absolute;
    border: solid #C2E1F5;
    border-width: 4px 0 0 4px;
    background: #88B7D5;
    content: '';
    width: 56px;
    height: 56px;
}

<div class="container container-decor">great distance</div>

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