diff --git a/src/subs_edit_box.cpp b/src/subs_edit_box.cpp
index 0f171cdfd..a7c3b5ea8 100644
--- a/src/subs_edit_box.cpp
+++ b/src/subs_edit_box.cpp
@@ -120,7 +120,7 @@ SubsEditBox::SubsEditBox(wxWindow *parent, agi::Context *context)
 	// Only supported in wxgtk
 	comment_box->SetCanFocus(false);
 #endif
-	top_sizer->Add(comment_box, 0, wxRIGHT | wxALIGN_CENTER, 5);
+	top_sizer->Add(comment_box, wxSizerFlags().Expand().Border(wxRIGHT, 5));
 
 	style_box = MakeComboBox("Default", wxCB_READONLY, &SubsEditBox::OnStyleChange, _("Style for this line"));
 
@@ -132,22 +132,22 @@ SubsEditBox::SubsEditBox(wxWindow *parent, agi::Context *context)
 			DialogStyleEditor(this, active_style, c, nullptr, "", font_list).ShowModal();
 		}
 	});
-	top_sizer->Add(style_edit_button, wxSizerFlags().Center().Border(wxRIGHT));
+	top_sizer->Add(style_edit_button, wxSizerFlags().Expand().Border(wxRIGHT));
 
 	actor_box = new Placeholder<wxComboBox>(this, _("Actor"), wxDefaultSize, wxCB_DROPDOWN | wxTE_PROCESS_ENTER, _("Actor name for this speech. This is only for reference, and is mainly useless."));
 	Bind(wxEVT_TEXT, &SubsEditBox::OnActorChange, this, actor_box->GetId());
 	Bind(wxEVT_COMBOBOX, &SubsEditBox::OnActorChange, this, actor_box->GetId());
-	top_sizer->Add(actor_box, wxSizerFlags(2).Center().Border(wxRIGHT));
+	top_sizer->Add(actor_box, wxSizerFlags(2).Expand().Border(wxRIGHT));
 
 	effect_box = new Placeholder<wxComboBox>(this, _("Effect"), wxDefaultSize, wxCB_DROPDOWN | wxTE_PROCESS_ENTER, _("Effect for this line. This can be used to store extra information for karaoke scripts, or for the effects supported by the renderer."));
 	Bind(wxEVT_TEXT, &SubsEditBox::OnEffectChange, this, effect_box->GetId());
 	Bind(wxEVT_COMBOBOX, &SubsEditBox::OnEffectChange, this, effect_box->GetId());
-	top_sizer->Add(effect_box, 3, wxALIGN_CENTER, 5);
+	top_sizer->Add(effect_box, wxSizerFlags(3).Expand());
 
 	char_count = new wxTextCtrl(this, -1, "0", wxDefaultPosition, wxDefaultSize, wxTE_READONLY | wxTE_CENTER);
 	char_count->SetInitialSize(char_count->GetSizeFromTextSize(GetTextExtent(wxS("000"))));
 	char_count->SetToolTip(_("Number of characters in the longest line of this subtitle."));
-	top_sizer->Add(char_count, 0, wxALIGN_CENTER, 5);
+	top_sizer->Add(char_count, wxSizerFlags().Expand());
 
 	// Middle controls
 	middle_left_sizer = new wxBoxSizer(wxHORIZONTAL);
@@ -160,7 +160,7 @@ SubsEditBox::SubsEditBox(wxWindow *parent, agi::Context *context)
 	layer->SetInitialSize(layer->GetSizeFromTextSize(GetTextExtent(wxS("00"))));
 #endif
 	layer->SetToolTip(_("Layer number"));
-	middle_left_sizer->Add(layer, wxSizerFlags().Center());
+	middle_left_sizer->Add(layer, wxSizerFlags().Expand());
 	middle_left_sizer->AddSpacer(5);
 
 	start_time = MakeTimeCtrl(_("Start time"), TIME_START);
@@ -197,13 +197,13 @@ SubsEditBox::SubsEditBox(wxWindow *parent, agi::Context *context)
 	split_box = new wxCheckBox(this,-1,_("Show Original"));
 	split_box->SetToolTip(_("Show the contents of the subtitle line when it was first selected above the edit box. This is sometimes useful when editing subtitles or translating subtitles into another language."));
 	split_box->Bind(wxEVT_CHECKBOX, &SubsEditBox::OnSplit, this);
-	middle_right_sizer->Add(split_box, wxSizerFlags().Center().Left());
+	middle_right_sizer->Add(split_box, wxSizerFlags().Expand());
 
 	// Main sizer
 	wxSizer *main_sizer = new wxBoxSizer(wxVERTICAL);
-	main_sizer->Add(top_sizer,0,wxEXPAND | wxALL,3);
-	main_sizer->Add(middle_left_sizer,0,wxEXPAND | wxLEFT | wxRIGHT | wxBOTTOM,3);
-	main_sizer->Add(middle_right_sizer,0,wxEXPAND | wxLEFT | wxRIGHT | wxBOTTOM,3);
+	main_sizer->Add(top_sizer, wxSizerFlags().Expand().Border(wxALL, 3));
+	main_sizer->Add(middle_left_sizer, wxSizerFlags().Expand().Border(wxLEFT | wxRIGHT | wxBOTTOM, 3));
+	main_sizer->Add(middle_right_sizer, wxSizerFlags().Expand().Border(wxLEFT | wxRIGHT | wxBOTTOM, 3));
 
 	// Text editor
 	edit_ctrl = new SubsTextEditCtrl(this, wxDefaultSize, wxBORDER_SUNKEN, c);
@@ -216,8 +216,8 @@ SubsEditBox::SubsEditBox(wxWindow *parent, agi::Context *context)
 	//      https://github.com/wangqr/Aegisub/issues/4
 	edit_ctrl->SetInitialSize(secondary_editor->GetSize());
 
-	main_sizer->Add(secondary_editor,1,wxEXPAND | wxLEFT | wxRIGHT | wxBOTTOM,3);
-	main_sizer->Add(edit_ctrl,1,wxEXPAND | wxLEFT | wxRIGHT | wxBOTTOM,3);
+	main_sizer->Add(secondary_editor, wxSizerFlags(1).Expand().Border(wxLEFT | wxRIGHT | wxBOTTOM, 3));
+	main_sizer->Add(edit_ctrl, wxSizerFlags(1).Expand().Border(wxLEFT | wxRIGHT | wxBOTTOM, 3));
 	main_sizer->Hide(secondary_editor);
 
 	bottom_sizer = new wxBoxSizer(wxHORIZONTAL);
@@ -265,7 +265,7 @@ wxTextCtrl *SubsEditBox::MakeMarginCtrl(wxString const& tooltip, int margin, wxS
 	ctrl->SetInitialSize(ctrl->GetSizeFromTextSize(GetTextExtent(wxS("0000"))));
 	ctrl->SetMaxLength(5);
 	ctrl->SetToolTip(tooltip);
-	middle_left_sizer->Add(ctrl, wxSizerFlags().Center());
+	middle_left_sizer->Add(ctrl, wxSizerFlags().Expand());
 
 	Bind(wxEVT_TEXT, [=](wxCommandEvent&) {
 		int value = agi::util::mid(-9999, atoi(ctrl->GetValue().utf8_str()), 99999);
@@ -282,7 +282,7 @@ TimeEdit *SubsEditBox::MakeTimeCtrl(wxString const& tooltip, TimeField field) {
 	ctrl->SetToolTip(tooltip);
 	Bind(wxEVT_TEXT, [=](wxCommandEvent&) { CommitTimes(field); }, ctrl->GetId());
 	ctrl->Bind(wxEVT_CHAR_HOOK, time_edit_char_hook);
-	middle_left_sizer->Add(ctrl, wxSizerFlags().Center());
+	middle_left_sizer->Add(ctrl, wxSizerFlags().Expand());
 	return ctrl;
 }
 
@@ -308,7 +308,7 @@ wxComboBox *SubsEditBox::MakeComboBox(wxString const& initial_text, int style, v
 	wxString styles[] = { "Default" };
 	wxComboBox *ctrl = new wxComboBox(this, -1, initial_text, wxDefaultPosition, wxDefaultSize, 1, styles, style | wxTE_PROCESS_ENTER);
 	ctrl->SetToolTip(tooltip);
-	top_sizer->Add(ctrl, wxSizerFlags(2).Center().Border(wxRIGHT));
+	top_sizer->Add(ctrl, wxSizerFlags(2).Expand().Border(wxRIGHT));
 	Bind(wxEVT_COMBOBOX, handler, this, ctrl->GetId());
 	return ctrl;
 }