text: class CompleteBtn {
      constructor() {
          this.txt = "Готово";
          cntx.font = "bold " + big_font_size + "px sans-serif";
          this.width = cntx.measureText(this.txt).width * cloud_txt_ratio;
          this.height = big_font_size * cloud_txt_ratio;
          this.x = cnvs_w / 2;
          this.y = cnvs_h - this.height;
          this.draw_trigger = false;
      }
      draw_complete() {
          cntx.beginPath();
  
          const half_w = this.width / 2;
          const half_h = this.height / 2;
          const half_PI = Math.PI / 2;
          cntx.arc(this.x - half_w + half_h, this.y, half_h, half_PI, - half_PI);
          cntx.arc(this.x + half_w - half_h, this.y, half_h, - half_PI, half_PI);
          cntx.lineTo(this.x - half_w + half_h, this.y + half_h);
          cntx.fillStyle = cloud_color;
          cntx.fill();
  
          cntx.closePath();
  
          cntx.fillStyle = txt_color;
          cntx.font = "bold " + big_font_size + "px sans-serif";
          cntx.textAlign = "center";
          cntx.textBaseline = "alphabetic";
          cntx.fillText(this.txt, this.x, this.y + big_font_size / 3);
      }
  }