Please follow the steps given below to implement Custom Fonts on your Moodle site.

Step 1) Download the font file from the internet which should be in the .ttf format
Step 2) Create a new folder inside where Edwiser RemUI theme is installed on your server. The path should be: moodle/theme/remui/fonts. Note: The folder name is fonts
Step 3) Now Copy-Paste the CSS mentioned below to the bottom of this file: /theme/remui/style/custom.css

@font-face {
font-family: '<font-name>';
font-style: normal;
font-weight: normal;
src: url('[[font:theme|<file-name>]]?v=');
src: url([[font:theme|<file-name>]]?v=) format('truetype');
}

body, span {
font-family: "<font-name>" !important;
}

h1,h2,h3,h4,h5,h6 {
font-family: "<font-name>";
}

.site-menubar {
font-family: "<font-name>";
}

<file-name> = Replace file name with the name of the font file name. For eg: MetalMacabre.ttf

<font-name> = Replace font name with the name of the Font. For eg: MetalMacabre

Step 4) Save the file and then you need do Purge Cache on your Moodle site.