1px

1px.js

if (window.devicePixelRatio && devicePixelRatio >= 2) {
    var testElem = document.createElement('div');
    testElem.style.border = '.5px solid transparent';
    document.body.appendChild(testElem);
    if (testElem.offsetHeight == 1) {
        document.documentElement.classList.add('hairlines');
    }
    document.body.removeChild(testElem);
}

hairlines.css

html.hairlines a, html.hairlines div, html.hairlines dl, html.hairlines header, html.hairlines ul, html.hairlines li {
    border-width: .5px!important;
}