@nobita In the CSS folder, there is a custom.css file (~/MagicMirror/css/custom.css). Any changes you make here will override the main font settings. You can adjust the font sizes here at your leisure.
For example:
body {
margin: 60px;
position: absolute;
height: calc(100% - 120px);
width: calc(100% - 120px);
background: #000;
color: #aaa;
font-family: "Roboto Condensed", sans-serif;
font-weight: 400;
font-size: 5em;
line-height: 3em;
-webkit-font-smoothing: antialiased;
}
… should give you a starting point.