Adding padding: 0 20px; doesn't work with added borders

[asasass]

How would I get it to work with added borders?

left side is 21px right side is 14px.

.tcell {
  display: table-cell;
  vertical-align: middle;
  padding: 0 20px;
}

padding: 0 20px;

Edit fiddle - JSFiddle - Code Playground

[Ray.H]

You should be using box-sizing: border-box

Try these amendments

html,
body {
  height: 100%;
  background: #000000;
  padding: 0;
  margin: 0;
  box-sizing: border-box; /*add this*/
}
 /*add this*/
*, *:before, *:after {
  box-sizing: inherit;
}

.outer {
  display: table;
  height: 100%;
  margin: 0 auto;
  width: 100%;
}

.tcell {
  display: table-cell;
  vertical-align: middle;
  padding: 0 20px;
}

[asasass]

This worked by itself:

Edit fiddle - JSFiddle - Code Playground

.video {
  border-radius: 25px;
  border: 3px solid green;
  box-sizing: border-box;
}