diff --git a/backend/app/controllers/posts_controller.rb b/backend/app/controllers/posts_controller.rb
index cc5afea..e8cae00 100644
--- a/backend/app/controllers/posts_controller.rb
+++ b/backend/app/controllers/posts_controller.rb
@@ -177,8 +177,8 @@ class PostsController < ApplicationController
     merge = bool?(:merge)
     return head :bad_request if force && merge
 
-    base_version_no = nil
-    base_version_no = parse_base_version_no unless force
+    base_version_no = parse_base_version_no
+    return head :bad_request if !(force) && !(base_version_no)
 
     title = params[:title].presence
     tag_names = params[:tags].to_s.split
@@ -442,9 +442,11 @@ class PostsController < ApplicationController
 
   def parse_base_version_no
     version_no = Integer(params[:base_version_no], exception: false)
-    raise ArgumentError, 'base_version_no は必須です．' unless version_no&.positive?
-
-    version_no
+    if version_no&.positive?
+      version_no
+    else
+      nil
+    end
   end
 
   def post_snapshot_from_version version
diff --git a/backend/app/services/version_recorder.rb b/backend/app/services/version_recorder.rb
index fe7c368..8175dba 100644
--- a/backend/app/services/version_recorder.rb
+++ b/backend/app/services/version_recorder.rb
@@ -16,7 +16,7 @@ class VersionRecorder
       @record = record_class.unscoped.lock.find(@record.id)
       latest = latest_version
 
-      validate_version_sequence! latest
+      validate_version_sequence!(latest)
 
       attrs = snapshot_attributes
 
@@ -27,7 +27,7 @@ class VersionRecorder
       version = version_class.create!(
           base_attributes(latest).merge(record_key => @record).merge(attrs))
 
-      update_record_version_no! version.version_no
+      update_record_version_no!(version.version_no)
 
       version
     end
@@ -47,7 +47,7 @@ class VersionRecorder
   end
 
   def update_record_version_no! version_no
-    @record.update_columns version_no: version_no
+    @record.update_columns(version_no:)
     @record.version_no = version_no
   end
 
diff --git a/frontend/src/components/PostEditForm.tsx b/frontend/src/components/PostEditForm.tsx
index 337ed08..d06b987 100644
--- a/frontend/src/components/PostEditForm.tsx
+++ b/frontend/src/components/PostEditForm.tsx
@@ -103,10 +103,16 @@ export default (({ post, onSave }: Props) => {
     e.preventDefault ()
 
     setDisabled (true)
-    await update ({ id: post.id, title, tags, parentPostIds,
-		    originalCreatedFrom, originalCreatedBefore },
-		  { baseVersionNo: post.versionNo })
-    setDisabled (false)
+    try
+    {
+      await update ({ id: post.id, title, tags, parentPostIds,
+		      originalCreatedFrom, originalCreatedBefore },
+		    { baseVersionNo: post.versionNo })
+    }
+    finally
+    {
+      setDisabled (false)
+    }
   }
 
   useEffect (() => {
@@ -114,7 +120,7 @@ export default (({ post, onSave }: Props) => {
   }, [post])
 
   return (
-      <div className="max-w-xl pt-2 space-y-4">
+      <form onSubmit={handleSubmit} className="max-w-xl pt-2 space-y-4">
 	{/* タイトル */}
 	<div>
 	  <Label>タイトル</Label>
@@ -154,10 +160,8 @@ export default (({ post, onSave }: Props) => {
 	{/* 送信 */}
 	<Button
 	    type="submit"
-	    disabled={disabled}
-	    onClick={handleSubmit}
-	    className="px-4 py-2 bg-blue-600 text-white rounded disabled:bg-gray-400">
+	    disabled={disabled}>
 	  更新
 	</Button>
-      </div>)
+      </form>)
 }) satisfies FC<Props>
diff --git a/frontend/src/components/PostFormTagsArea.tsx b/frontend/src/components/PostFormTagsArea.tsx
index b23e121..58e0db4 100644
--- a/frontend/src/components/PostFormTagsArea.tsx
+++ b/frontend/src/components/PostFormTagsArea.tsx
@@ -31,13 +31,12 @@ const replaceToken = (value: string, start: number, end: number, text: string) =
     `${ value.slice (0, start) }${ text }${ value.slice (end) }`
 
 
-type Props =
-    & { tags:     string
-	setTags:  (tags: string) => void }
-    & ComponentPropsWithoutRef<'textarea'>
+type Props = Omit<ComponentPropsWithoutRef<'textarea'>, 'value' | 'onChange' | 'onBlur'> & {
+    tags:     string
+    setTags:  (tags: string) => void }
 
 
-export default (({ tags, setTags, ...rest }: Props) => {
+export default (({ tags, setTags, onBlur, ...rest }: Props) => {
   const ref = useRef<HTMLTextAreaElement> (null)
 
   const [bounds, setBounds] = useState<{ start: number; end: number }> ({ start: 0, end: 0 })
@@ -77,6 +76,7 @@ export default (({ tags, setTags, ...rest }: Props) => {
       <div className="relative w-full">
 	<Label>タグ</Label>
 	<TextArea
+	    {...rest}
 	    ref={ref}
 	    value={tags}
 	    onChange={ev => setTags (ev.target.value)}
@@ -85,11 +85,11 @@ export default (({ tags, setTags, ...rest }: Props) => {
 	      await recompute (pos)
 	    }}
 	    onFocus={() => setFocused (true)}
-	    onBlur={() => {
+	    onBlur={ev => {
 	      setFocused (false)
 	      setSuggestionsVsbl (false)
-	    }}
-	    {...rest}/>
+	      onBlur?.(ev)
+	    }}/>
 	{focused && (
 	    <TagSearchBox
 		suggestions={suggestionsVsbl && suggestions.length > 0
diff --git a/frontend/src/components/common/DateTimeField.tsx b/frontend/src/components/common/DateTimeField.tsx
index 29e4d19..e97b96f 100644
--- a/frontend/src/components/common/DateTimeField.tsx
+++ b/frontend/src/components/common/DateTimeField.tsx
@@ -34,6 +34,7 @@ export default (({ value, onChange, className, onBlur, ...rest }: Props) => {
 
   return (
       <input
+	  {...rest}
 	  className={cn ('border rounded p-2', className)}
 	  type="datetime-local"
 	  value={local}
@@ -42,6 +43,5 @@ export default (({ value, onChange, className, onBlur, ...rest }: Props) => {
 	    setLocal (v)
 	    onChange?.(v ? (new Date (v)).toISOString () : null)
 	  }}
-	  onBlur={onBlur}
-	  {...rest}/>)
+	  onBlur={onBlur}/>)
 }) satisfies FC<Props>
diff --git a/frontend/src/components/dialogues/DialogueProvider.tsx b/frontend/src/components/dialogues/DialogueProvider.tsx
index 8cb0990..3d20a9e 100644
--- a/frontend/src/components/dialogues/DialogueProvider.tsx
+++ b/frontend/src/components/dialogues/DialogueProvider.tsx
@@ -5,6 +5,7 @@ import { Dialog,
 	 DialogContent,
 	 DialogDescription,
 	 DialogFooter,
+	 DialogHeader,
 	 DialogTitle } from '@/components/ui/dialog'
 
 import type { FC, ReactNode } from 'react'
@@ -118,13 +119,15 @@ export default (({ children }: Props) => {
 		closeActive (active?.kind !== 'confirm' && null)
 	    }}>
 	  {active && (
-	      <DialogContent>
-		<DialogTitle>{active.options.title}</DialogTitle>
-
-		{active.options.description && (
-		    <DialogDescription asChild>
-		      <div>{active.options.description}</div>
-		    </DialogDescription>)}
+	      <DialogContent className="px-6 pb-6 pt-7">
+		<DialogHeader className="pl-8">
+		  <DialogTitle>{active.options.title}</DialogTitle>
+
+		  {active.options.description && (
+		      <DialogDescription asChild>
+			<div>{active.options.description}</div>
+		      </DialogDescription>)}
+		</DialogHeader>
 
 		<DialogFooter>
 		  {active.kind === 'confirm' && (
diff --git a/frontend/src/components/ui/button.tsx b/frontend/src/components/ui/button.tsx
index 36496a2..34abd10 100644
--- a/frontend/src/components/ui/button.tsx
+++ b/frontend/src/components/ui/button.tsx
@@ -4,34 +4,47 @@ import { cva, type VariantProps } from "class-variance-authority"
 
 import { cn } from "@/lib/utils"
 
-const buttonVariants = cva(
-  "inline-flex items-center justify-center gap-2 whitespace-nowrap rounded-md text-sm font-medium ring-offset-background transition-colors focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring focus-visible:ring-offset-2 disabled:pointer-events-none disabled:opacity-50 [&_svg]:pointer-events-none [&_svg]:size-4 [&_svg]:shrink-0",
+const buttonVariants = cva (
+  [
+    'inline-flex items-center justify-center gap-2 whitespace-nowrap',
+    'rounded-md text-sm font-medium transition-colors',
+    'focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-slate-400',
+    'disabled:pointer-events-none disabled:opacity-50',
+    '[&_svg]:pointer-events-none [&_svg]:size-4 [&_svg]:shrink-0',
+  ].join (' '),
   {
     variants: {
       variant: {
-        default: "bg-primary text-primary-foreground hover:bg-primary/90",
+        default:
+          'bg-slate-900 text-white hover:bg-slate-700 dark:bg-slate-100 dark:text-slate-900 dark:hover:bg-slate-300',
+
         destructive:
-          "bg-destructive text-destructive-foreground hover:bg-destructive/90",
+          'bg-red-600 text-white hover:bg-red-700 dark:bg-red-700 dark:hover:bg-red-600',
+
         outline:
-          "border border-input bg-background hover:bg-accent hover:text-accent-foreground",
+          'border border-slate-300 bg-white text-slate-900 hover:bg-slate-100 dark:border-slate-700 dark:bg-slate-900 dark:text-slate-100 dark:hover:bg-slate-800',
+
         secondary:
-          "bg-secondary text-secondary-foreground hover:bg-secondary/80",
-        ghost: "hover:bg-accent hover:text-accent-foreground",
-        link: "text-primary underline-offset-4 hover:underline",
+          'bg-slate-100 text-slate-900 hover:bg-slate-200 dark:bg-slate-800 dark:text-slate-100 dark:hover:bg-slate-700',
+
+        ghost:
+          'text-slate-900 hover:bg-slate-100 dark:text-slate-100 dark:hover:bg-slate-800',
+
+        link:
+          'text-blue-700 underline-offset-4 hover:underline dark:text-blue-300',
       },
       size: {
-        default: "h-10 px-4 py-2",
-        sm: "h-9 rounded-md px-3",
-        lg: "h-11 rounded-md px-8",
-        icon: "h-10 w-10",
+        default: 'h-10 px-4 py-2',
+        sm:      'h-9 rounded-md px-3',
+        lg:      'h-11 rounded-md px-8',
+        icon:    'h-10 w-10',
       },
     },
     defaultVariants: {
-      variant: "default",
-      size: "default",
+      variant: 'default',
+      size:    'default',
     },
-  }
-)
+  })
 
 export interface ButtonProps
   extends React.ButtonHTMLAttributes<HTMLButtonElement>,
diff --git a/frontend/src/components/ui/dialog.tsx b/frontend/src/components/ui/dialog.tsx
index 08dbbf8..0eb3096 100644
--- a/frontend/src/components/ui/dialog.tsx
+++ b/frontend/src/components/ui/dialog.tsx
@@ -50,14 +50,16 @@ const DialogContent = React.forwardRef<
       {...props}
     >
       {children}
+
       <DialogPrimitive.Close
 	  className={cn (
-	      'absolute right-4 top-4 rounded-full p-1',
-	      'text-muted-foreground opacity-70 transition-opacity',
-	      'hover:bg-accent hover:text-accent-foreground hover:opacity-100',
-	      'focus:outline-none focus:ring-2 focus:ring-ring focus:ring-offset-2')}>
+	      'absolute left-4 top-4 rounded-full p-1',
+	      'text-slate-500 transition-colors',
+	      'hover:bg-slate-200 hover:text-slate-900',
+	      'dark:text-slate-400 dark:hover:bg-slate-700 dark:hover:text-slate-50',
+	      'focus:outline-none focus:ring-2 focus:ring-slate-400')}>
 	<X className="h-4 w-4"/>
-	<span className="sr-only">Close</span>
+	<span className="sr-only">閉ぢる</span>
       </DialogPrimitive.Close>
     </DialogPrimitive.Content>
   </DialogPortal>