Rotate the rectangular element 90 degrees along the grid

Question

I am doing a webapp where you can place elements in a grid, move them and rotate.

I ran into the problem of rotating elements if the width is an odd number and the height is even and vice versa.

When rotating around the center of an element, the new coordinates for the element end in half.

Rotation happens when im adds a class to an element using jQuery and the actual rotation is done using CSS.

I need the element to align with the grid after an "erroneous" rotation. How can I achieve this?

Answer 1

CSS , origin tranform, . 5 * 2 :

transform-origin: 40% 50%;

DEMO ( )

*{box-sizing:border-box;margin:0;padding:0;}
.b{
    float:left;
    width:9.5vw;
    height:9.5vw;
    background:#262C33;
    border:1px solid grey;
}

.r{
    position:absolute;
    left:19vw; top: 28.5vw;
    width:47.5vw; height:19vw;
    border:2px solid #fff;
}
.r:hover{
    transform-origin: 40% 50%;
    transform:rotate(90deg);
}

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