implement marathon start screen

menus/marathon_start.gd

@@ -4,11 +4,31 @@ extends Control
 export var first_level: PackedScene
 
 
+onready var difficulty_buttons := [
+	$"%BeginnerButton",
+	$"%AdvancedButton",
+	$"%AdvancedButton",
+	$"%ProfessionalButton",
+]
+
+
 func _ready() -> void:
+	yield(get_tree(), "idle_frame")
+	difficulty_buttons[Game.difficulty].grab_focus()
 	Fade.fade_in()
 
 
 func _input(event: InputEvent) -> void:
 	if Input.is_action_just_pressed("ui_accept"):
+		Game.lives = Game.marathon_lives
 		Game.marathon_score = 0
+		Game.marathon_shards = 0
 		Game.change_map(first_level)
+
+
+func _set_difficulty(difficulty: int) -> void:
+	Game.difficulty = difficulty
+
+
+func _on_DifficultySelect_focus_entered() -> void:
+	difficulty_buttons[Game.difficulty].grab_focus()