Adding styles directly into the page template from the controller

css.php

<?php 

// An example of how to generate inpage css for body 

// Typically saved in a database OR in theme folder as style.custom.css
$encodedStyles = json_encode([
    'body' => [
        'font-family' => '"NeutraText-Book"',
        'font-size' => '14px',
        'background-color' => 'rgba(255, 255, 255, 1)',
    ],
    'h1' => [
        'color' => '#000'
    ],
    '.container' => [
        'max-width' => '1180px',
    ],
]);

// Data from the database OR custom file 
$styles = json_decode($encodedStyles);

$css = ''; // Declared variable 

foreach($styles as $selector => $declarations){
    $css .= $selector . '{' . PHP_EOL;
    foreach($declarations as $prop => $value){
        $css .= $prop . ':' . $value . ';' . PHP_EOL;
    }
    $css .= '}' . PHP_EOL;
}

$this->output->set_header('Content-Type', 'text/css');
$this->output->set_output($css);

https://jsfiddle.net/1mqejb87/