after html to pdf, the drop-shadow missed.

[bk111]

a1.css

body img{
border-radius: 20px; /* 圆角 /
-webkit-filter: drop-shadow(10px 10px 10px #4444dd);
filter: drop-shadow(10px 10px 10px #4444dd);
margin-top: 20px; / 在图片上方添加10像素的空行 /
margin-bottom: 20px; / 在图片下方添加10像素的空行 */
}

wkhtmltopdf_options = {
'dpi': 600,
# 'page-size': 'A4',
# 'margin-top': '15mm',
"user-style-sheet": "a1.css",
'debug-javascript': [''],
'debug-javascript': True,
'javascript-delay': 10000,
'header-html': 'header.html',
#'header-line': '',
'footer-html': 'footer.html',
'footer-right': '[page]/[topage]', #在页脚加页码
'no-stop-slow-scripts': True,
'load-media-error-handling': 'skip',
'load-error-handling': 'skip',
'enable-local-file-access': True
}

There is drop-shadow picture in html, but no drop-shadow in pdf, why?