how to set width with padding code example

Example 1: width 100% with padding

.content {
    width: 100%;
    box-sizing: border-box;
}

Example 2: applying padding increases the size of the element

/* apply a natural box layout model to all elements, but allowing components to change */
html {
  box-sizing: border-box;
}
*, *:before, *:after {
  box-sizing: inherit;
}