I bisected this regression to 7daf5cd

Invaliding when pseudo-element style changes revealed another issue that scroll_by here should not cause relayout, because it results in infinite recursion:

    // Scrolling by zero offset will clamp scroll offset back to valid range if it was out of bounds
    // after the viewport size change.
    if (auto window = this->window())
        window->scroll_by(0, 0);

Part of stacktrace:

    frame #701: 0x0000000107ea74f8 liblagom-web.0.dylib`::scroll_by() at Window.cpp:1376:5 [opt]
    frame #702: 0x0000000107ea757c liblagom-web.0.dylib`::scroll_by() at Window.cpp:1395:5 [opt]
    frame #703: 0x0000000107c9896c liblagom-web.0.dylib`::update_layout() at Document.cpp:1153:17 [opt]
    frame #704: 0x0000000107ea71b8 liblagom-web.0.dylib`::scroll() at Window.cpp:1309:15 [opt]
    frame #705: 0x0000000107ea74f8 liblagom-web.0.dylib`::scroll_by() at Window.cpp:1376:5 [opt]
    frame #706: 0x0000000107ea757c liblagom-web.0.dylib`::scroll_by() at Window.cpp:1395:5 [opt]
    frame #707: 0x0000000107c9896c liblagom-web.0.dylib`::update_layout() at Document.cpp:1153:17 [opt]
    frame #708: 0x0000000107ea71b8 liblagom-web.0.dylib`::scroll() at Window.cpp:1309:15 [opt]
    frame #709: 0x0000000107ea74f8 liblagom-web.0.dylib`::scroll_by() at Window.cpp:1376:5 [opt]
    frame #710: 0x0000000107ea757c liblagom-web.0.dylib`::scroll_by() at Window.cpp:1395:5 [opt]
    frame #711: 0x0000000107c9896c liblagom-web.0.dylib`::update_layout() at Document.cpp:1153:17 [opt]
    frame #712: 0x0000000107ea71b8 liblagom-web.0.dylib`::scroll() at Window.cpp:1309:15 [opt]
    frame #713: 0x0000000107ea74f8 liblagom-web.0.dylib`::scroll_by() at Window.cpp:1376:5 [opt]
    frame #714: 0x0000000107ea757c liblagom-web.0.dylib`::scroll_by() at Window.cpp:1395:5 [opt]
    frame #715: 0x0000000107c9896c liblagom-web.0.dylib`::update_layout() at Document.cpp:1153:17 [opt]
    frame #716: 0x0000000107ea71b8 liblagom-web.0.dylib`::scroll() at Window.cpp:1309:15 [opt]
    frame #717: 0x0000000107ea74f8 liblagom-web.0.dylib`::scroll_by() at Window.cpp:1376:5 [opt]
    frame #718: 0x0000000107ea757c liblagom-web.0.dylib`::scroll_by() at Window.cpp:1395:5 [opt]
    frame #719: 0x0000000107c9896c liblagom-web.0.dylib`::update_layout() at Document.cpp:1153:17 [opt]
    frame #720: 0x0000000107ea71b8 liblagom-web.0.dylib`::scroll() at Window.cpp:1309:15 [opt]
    frame #721: 0x0000000107ea74f8 liblagom-web.0.dylib`::scroll_by() at Window.cpp:1376:5 [opt]
    frame #722: 0x0000000107ea757c liblagom-web.0.dylib`::scroll_by() at Window.cpp:1395:5 [opt]
    frame #723: 0x0000000107c9896c liblagom-web.0.dylib`::update_layout() at Document.cpp:1153:17 [opt]
    frame #724: 0x0000000107ea71b8 liblagom-web.0.dylib`::scroll() at Window.cpp:1309:15 [opt]
    frame #725: 0x0000000107ea74f8 liblagom-web.0.dylib`::scroll_by() at Window.cpp:1376:5 [opt]
    frame #726: 0x0000000107ea757c liblagom-web.0.dylib`::scroll_by() at Window.cpp:1395:5 [opt]
    frame #727: 0x0000000107c9896c liblagom-web.0.dylib`::update_layout() at Document.cpp:1153:17 [opt]
    frame #728: 0x0000000107ea71b8 liblagom-web.0.dylib`::scroll() at Window.cpp:1309:15 [opt]
    frame #729: 0x0000000107ea74f8 liblagom-web.0.dylib`::scroll_by() at Window.cpp:1376:5 [opt]
    frame #730: 0x0000000107ea757c liblagom-web.0.dylib`::scroll_by() at Window.cpp:1395:5 [opt]
    frame #731: 0x0000000107c9896c liblagom-web.0.dylib`::update_layout() at Document.cpp:1153:17 [opt]
    frame #732: 0x0000000107ea71b8 liblagom-web.0.dylib`::scroll() at Window.cpp:1309:15 [opt]
    frame #733: 0x0000000107ea74f8 liblagom-web.0.dylib`::scroll_by() at Window.cpp:1376:5 [opt]
    frame #734: 0x0000000107ea757c liblagom-web.0.dylib`::scroll_by() at Window.cpp:1395:5 [opt]
    frame #735: 0x0000000107c9896c liblagom-web.0.dylib`::update_layout() at Document.cpp:1153:17 [opt]
    frame #736: 0x0000000107ea71b8 liblagom-web.0.dylib`::scroll() at Window.cpp:1309:15 [opt]
    frame #737: 0x0000000107ea74f8 liblagom-web.0.dylib`::scroll_by() at Window.cpp:1376:5 [opt]
    frame #738: 0x0000000107ea757c liblagom-web.0.dylib`::scroll_by() at Window.cpp:1395:5 [opt]
    frame #739: 0x0000000107c9896c liblagom-web.0.dylib`::update_layout() at Document.cpp:1153:17 [opt]
    frame #740: 0x0000000107d92f9c liblagom-web.0.dylib`::process() [inlined] operator() at EventLoop.cpp:293:22 [opt]
    frame #741: 0x0000000107d92f94 liblagom-web.0.dylib`::process() [inlined] operator()<(lambda at /Users/kalenik/ladybird/Userland/Libraries/LibWeb/HTML/EventLoop/EventLoop.cpp:285:44)> at EventLoop.cpp:201:17 [opt]
    frame #742: 0x0000000107d92f28 liblagom-web.0.dylib`::process() at EventLoop.cpp:285:5 [opt]
    frame #743: 0x0000000107f899f4 liblagom-web.0.dylib`::call() [inlined] operator() at SafeFunction.h:85:25 [opt]
    frame #744: 0x0000000107f899d8 liblagom-web.0.dylib`::call() [inlined] operator() at TimerSerenity.cpp:23:13 [opt]
    frame #745: 0x0000000107f899b0 liblagom-web.0.dylib`::call() at Function.h:187:20 [opt]
    frame #746: 0x0000000104aa4320 liblagom-core.0.dylib`::operator()() at Function.h:120:25 [opt]
    frame #747: 0x0000000104aa37ec liblagom-core.0.dylib`::dispatch_event() at EventReceiver.cpp:162:17 [opt]
    frame #748: 0x00000001041131c0 WebContent`::impl() [inlined] qt_timer_fired at EventLoopImplementationQt.cpp:219:12 [opt]