手机端375设计稿自动转换，最大尺寸不超过750

(function flexible(window, document) {
const docEl = document.documentElement;
const dpr = window.devicePixelRatio || 1;

// adjust body font size
function setBodyFontSize() {
if (document.body) {
document.body.style.fontSize = 12 + 'px';
} else {
document.addEventListener('DOMContentLoaded', setBodyFontSize);
}
}
setBodyFontSize();

// set 1rem = viewWidth / 10
function setRemUnit() {
const rem = (docEl.clientWidth > 750 ? 750 : docEl.clientWidth) / 10;
docEl.style.fontSize = rem > 40 ? '40px' : rem + 'px';
}

setRemUnit();

// reset rem unit on page resize
window.addEventListener('resize', setRemUnit);
window.addEventListener('pageshow', function(e) {
if (e.persisted) {
setRemUnit();
}
});

// detect 0.5px supports
if (dpr >= 2) {
const fakeBody = document.createElement('body');
const testElement = document.createElement('div');
testElement.style.border = '.5px solid transparent';
fakeBody.appendChild(testElement);
docEl.appendChild(fakeBody);
if (testElement.offsetHeight === 1) {
docEl.classList.add('hairlines');
}
docEl.removeChild(fakeBody);
}
})(window, document);