Reading a value of css styles using nodejs

You can use postcss to parse the css and get the values you want.

Here is an example of how to get min and max width from different css files (for the same selector table[my-type="myStyle"]):

const fs = require('fs');
const postcss = require('postcss');

const allWidthValues = [];

const files = [
    'styles/style-1.css',
    'styles/style-2.css',
    'styles/style-3.css'
];

const selector = 'table[my-type="myStyle"]';

const processor = postcss.plugin('processor', () => (css) => {    
    // Callback for each rule node.
    css.walkRules((rule) => {        
        // Match the individual rule selector 
        if (rule.selector.indexOf(selector) !== -1) {
            // Callback for each declaration.
            rule.walkDecls(decl => {
                // Find the width declaration
                if(decl.prop.indexOf('width') !== -1) {
                    const width = decl.value.replace('px', '') * 1;
                    allWidthValues.push(width);
                }
            })
        }
    });
});

files.forEach(file => {
    const css = fs.readFileSync(file, 'utf-8');
    postcss([processor])
        .process(css, {from : file})
        .then(() => console.log('Done processing file : ', file))
        .catch(() => console.log('Error processing file : ', file));    

});

console.log('All width values : ', allWidthValues);

allWidthValues.sort();

console.log('Min width : ', allWidthValues[0]);
console.log('Max width : ', allWidthValues[allWidthValues.length - 1]);