Text rendering issue in Pygame

Question

I'm trying to make a HUD with the player's HP displayed in it. For some reason, the text is not appearing despite the code executing correctly. I am using my Button class to render this text for efficiency's sake, even though the HUD is never actually interacted with using the mouse. Here is the Button class followed by the HUD class:

class Button:
    def __init__(self, x, y, width, height, fg, bg, content, fontsize):
        self.font = pygame.font.Font('Assets/PixelOperator-Bold.ttf', 32)
        self.content = content
        self.x = x
        self.y = y
        self.width = width
        self.height = height
        self.fg = fg
        self.bg = bg

        self._layer = 5
        self.image = pygame.Surface((self.width, self.height))
        self.image.fill(self.bg)
        self.rect = self.image.get_rect()
        self.rect.x = self.x
        self.rect.y = self.y

        self.text = self.font.render(self.content, True, self.fg)
        self.text_rect = self.text.get_rect(center=(self.width/2, self.height/2))
        self.image.blit(self.text, self.text_rect)

    def is_pressed(self, pos, pressed):
        if self.rect.collidepoint(pos):
            if pressed[0]:
                return True
            return False
        return False

class hud (pygame.sprite.Sprite):
    def __init__(self, game, hudx, hudy):

        self.game = game
        self._layer = 3
        self.groups = self.game.all_sprites
        pygame.sprite.Sprite.__init__(self, self.groups)

        self.hudx = 0
        self.hudy = 0

        self.width = WinWidth
        self.height = 80
        self.image = pygame.Surface([self.width, self.height])
        self.image.fill(black)
        self.rect = self.image.get_rect()

        #self.hpdisplay = Button(10, 100, 100, 50, white, black, 'HP: {n}', 32)
        self.hpdisplay = game.font.render('HP: 100', True, white)
        self.hpdisplay.rect = self.hpdisplay.get_rect(x=10, y=10)
        game.screen.blit(self.hpdisplay, self.hpdisplay.rect)```

Here's an instance of this button class working:

def intro_screen(self):
        intro = True

        title = self.font.render('Cambria', True, white)
        title_rect = title.get_rect(x=10, y=10)
        pygame.mixer.music.play(-1)

        play_button = Button(-5, 100, 100, 50, white, black, 'PLAY', 32)

        while intro:
            for event in pygame.event.get():
                if event.type == pygame.QUIT:
                    intro = False
                    self.running = False

            mouse_pos = pygame.mouse.get_pos()
            mouse_pressed = pygame.mouse.get_pressed()

            if play_button.is_pressed(mouse_pos, mouse_pressed):
                pygame.mixer.music.fadeout(500)
                intro = False

            self.screen.blit(self.intro_background, (0, 0))
            self.screen.blit(title, title_rect)
            self.screen.blit(play_button.image, play_button.rect)
            self.clock.tick(FPS)
            pygame.display.update()