How to prevent a element from being resized when zooming

I'm building my website, and i have a problem with a div box. I would like to find a way to freeze that div, so it cannot be resized when someone zoom in.

I already have position fixed, and i know that i could use width 100%, but if i do that it won't keep the aspect ratio if someone resize the window. I tried to use vw and vh but id didn't solve my problem :/ I searched a lot on internet but i can't find a way that work for me.

Here is my code :

.wmenu {
position: fixed;
left:        50%;
top:         50%;
width:       180px;
height:      180px;
margin-left: -90px;
margin-top:  -67px; 
background-color: rgb(13, 70, 155) ;
border-radius: 50%;

}

Can someone help me please ?