If you don't want invert color

dash-dark-mode-patch.m

// clang -shared -undefined dynamic_lookup -o /Applications/Dash.app/Contents/MacOS/libDash.dylib Dash.m
// optool install -c load -p @executable_path/libDash.dylib -t /Applications/Dash.app/Contents/MacOS/Dash

#import <Foundation/Foundation.h>
#import <objc/runtime.h>

static void pleasedontinvertwebview(/* we don't care about the args */) {
  NSLog(@"oops");
}

static void pleasedontinvertimages(id self, id sel, NSURL *url) {
  NSError *err = nil;
  NSString *content = [NSString stringWithContentsOfURL:url encoding:NSUTF8StringEncoding error:&err];
  if (err) return;
  NSArray *lines = [content componentsSeparatedByString:@"\n"];
  NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF contains[c] 'invert()'"];
  NSArray *filtered = [lines filteredArrayUsingPredicate:predicate];
  NSString *style = [filtered componentsJoinedByString:@"\n"];
  [style writeToURL:url atomically:YES encoding:NSUTF8StringEncoding error:nil];
}

__attribute__((constructor)) static void webview() {
  return;
  Method m = class_getInstanceMethod(NSClassFromString(@"DHWebView"),
                                     NSSelectorFromString(@"setContentFilters:"));
  if (m) method_setImplementation(m, (IMP)pleasedontinvertwebview);
  m = class_getInstanceMethod(NSClassFromString(@"WebPreferences"),
                                     NSSelectorFromString(@"setUserStyleSheetLocation:"));
  if (m) method_setImplementation(m, (IMP)pleasedontinvertimages);
}