use calc css code example
Example 1: css calc
body {
width: calc(100vw - 8px);
height: calc(100vh - 8px);
}
Example 2: calc() css
.banniere {
position: absolute;
left: 40px;
width: calc(40px - 80px);
border: solid black 1px;
box-shadow: 1px 2px;
background-color: yellow;
padding: 6px;
text-align: center;
box-sizing: border-box;
}